36 results on '"Dobbidi Pamu"'
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2. Structural and Thermal Study of Mg2TiO4 Nanoparticles Synthesized by Mechanical Alloying Method
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Dobbidi Pamu, B. K. Sahoo, Ashish K. Sarangi, and R. K. Bhuyan
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010302 applied physics ,Materials science ,Chemical engineering ,0103 physical sciences ,Thermal ,Nanoparticle ,02 engineering and technology ,Building and Construction ,021001 nanoscience & nanotechnology ,0210 nano-technology ,01 natural sciences - Abstract
Background: Mg2TiO4 – based ceramics have proven their potentiality in the field of wireless communication systems. In the past, Mg2TiO4 ceramics was considered a quite optical response material in thin film form. Moreover, there is very few studies have been done whatever the proposed work in the present study. Objective: To prepare Mg2TiO4 nano-powders with the help of High Energy Ball Mill (HEBM) and intend to investigate its effect on crystal structure, microstructure and on thermodynamic behavior of MgO-TiO2 system. Methods: Mg2TiO4 ceramics were synthesized using Mechanical alloying method from high- purity oxides MgO and TiO2 (99.99%) of Sigma Aldrich (St. Louis, MO). Results: From the experimental studies it is observed that the powder’s particle size decreases with an increase of milling time. XRD analysis is carried out for phase confirmation of the mixed Mg2TiO4 powder. Further, the result also showed that there is structural changes occurred in the sample by high energy ball milling process, milled at different times. The nanocrystalline nature Mg2TiO4 powder was confirmed from microstructure taken by Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM). Further, differential thermal gravimetric analysis has been carried out to investigate the thermal behavior of milled Mg2TiO4 -powder (35 hours). Conclusion: In work, the effect of mechanical alloying on structural, microstructural and thermal properties of nanocrystalline Mg2TiO4 powders has been investigated systematically. The effect of milling time on particle size, crystal structure and the microstructure was studied using XRD, FE-SEM, TEM and DSC/TGA analysis. The microstructural analysis (FE-SEM and TEM) reveals the nanocrystallinity nature of MTO ceramics prepared by mechanical alloying method. The thermal decomposition behavior of the milled powders was examined by a Thermo-Gravimetric Analyzer (TGA) in argon atmosphere. more...
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- 2020
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3. Structural, Electrical, and AC-Resistivity Studies of BNT-KN Piezoelectric Ceramics
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Srinivas Pattipaka, Sweety Bora, and Dobbidi Pamu
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010302 applied physics ,Materials science ,Composite number ,Conductance ,02 engineering and technology ,Dielectric ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Piezoelectricity ,Electronic, Optical and Magnetic Materials ,Electrical resistivity and conductivity ,visual_art ,0103 physical sciences ,visual_art.visual_art_medium ,Ceramic ,Composite material ,0210 nano-technology ,Sol-gel - Abstract
The lead-free (1 – x) Bi0.5Na0.5TiO3 – x KNbO3 (BNT-KN; x = 0 – 0.12) composite ceramics have been synthesized by a sol-gel process. Their structure, morphology, AC conductance and dielectric response were studied systematically. The X-ray diffraction patterns of BNT-KN revealed a morphotropic phase boundary between a rhombohedral and a pseudocubic structure. The temperature-dependent dielectric response of pure BNT revealed two-phase transitions at 200 °C (TR-T or Td) and 320 °C (TC). Furthermore, the critical temperatures were found to shift to lower values with increasing KN concentration. The manifested relaxor behavior was well confirmed by a modified Curie – Weiss law. The hopping conduction mechanism in BNT-KN was characterized through AC-resistivity analysis. more...
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- 2020
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4. Effect of oxygen partial pressure on nonlinear optical and electrical properties of BNT–KNNG composite thin films
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Gyan Prakash Bharti, Srinivas Pattipaka, J. Pundareekam Goud, Dobbidi Pamu, Alika Khare, and K. C. James Raju
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010302 applied physics ,Materials science ,Analytical chemistry ,Dielectric ,Condensed Matter Physics ,01 natural sciences ,Space charge ,Ferroelectricity ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Pulsed laser deposition ,Crystallinity ,Tetragonal crystal system ,Phase (matter) ,0103 physical sciences ,Electrical and Electronic Engineering ,Refractive index - Abstract
Composite thin films of 1–x [Bi0.5Na0.5TiO3] – x [K0.5Na0.5NbO3 + 1 wt% Gd2O3] (BNT–KNNG); (x = 0.01) have been deposited at various O2 pressures from 0.1 to 10 Pa by pulsed laser deposition, and their crystal structure, surface morphology, optical, dielectric, and ferroelectric properties were investigated. X-ray diffraction analysis of thin films deposited at 0.1 Pa revealed a single phase of BNT–KNNG and further (> 0.1 Pa), film crystallinity gradually increased with a rise in O2 pressure. The improvement in the refractive index and a reduction in optical bandgap are observed with O2 pressure and are estimated to be 2.28–2.42 and 4.08–3.65 eV, respectively. The third-order nonlinear optical coefficients estimated using the Z-scan technique are found to be enhanced with O2 pressure. The film deposited at 10 Pa exhibited a higher nonlinear refractive index (n2 = 6.188 × 10− 6 cm2/W) and a strong absorption coefficient (β = 1.043 cm/W). The temperature-dependent dielectric response displayed two structural phase transitions from rhombohedral to tetragonal phase at 165 oC and tetragonal to cubic phase at 298 oC. The enhanced dielectric (er = 411, tanδ = 0.156 @ 1 kHz), Microwave dielectric (er = 317 and tanδ = 0.0074 @ 10 GHz), and ferroelectric (Pr = 25.31 µC/cm2, EC = 42.62 kV/cm @ 1 kHz) properties with low leakage current are observed for the film deposited at 10 Pa which followed a space charge limited conduction behavior. The obtained microwave and nonlinear optical properties of BNT–KNNG composite films are suitable for tunable microwave and optical photonic device applications. more...
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- 2020
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5. Influence of high-energy ball milling on structural, microstructural, and optical properties of Mg2TiO4 nanoparticles
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Ranjan K. Mohapatra, Dobbidi Pamu, B. K. Sahoo, G. Nath, Debadutta Das, and R. K. Bhuyan
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010302 applied physics ,Materials science ,Photoluminescence ,Band gap ,Scanning electron microscope ,Analytical chemistry ,Nanoparticle ,Condensed Matter Physics ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Nanocrystalline material ,Electronic, Optical and Magnetic Materials ,Transmission electron microscopy ,0103 physical sciences ,Crystallite ,Electrical and Electronic Engineering ,Ball mill - Abstract
In this paper, we report the impact of mechanical activation on structural, microstructural, thermal, and optical properties of Mg2TiO4 (MTO) nanoparticles prepared by high-energy ball milling. Williamson–Hall (W–H) method was carried out in order to understand the origin of the broadening in the X-ray diffraction (XRD) peaks and for the estimation of crystallite size of MTO nanocrystalline powder. It is revealed that the peak broadening is not only due to reduced coherently diffracting domain size but also due to a significant strain distribution. The calculated strain was 9.0 × 10−3 and the average crystallite sizes are 40–60 nm for 35-h milled powder and this result is consistent with transmission electron microscopy (TEM) analysis. To examine the nature of lattice fringes for the 35-h milled samples, high-resolution TEM study was carried out. It revealed that the as-prepared samples are highly crystalline in nature. The surface morphological studies were carried out by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Further, MTO nanoparticles showed a strong absorption at ~ 356 nm, and the bandgap values ranged between 3.26 and 3.78 eV with an increase of milling time from 0 to 35 h. The photoluminescence (PL) spectrum measured at room temperature showed the bands which are belong to the near band edge emission at 357 nm. The MTO nanoparticles prepared by mechanical alloying method exhibited promising optical properties which are suitable for commercial optoelectronic applications. more...
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- 2019
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6. Effect of thermal treatment on the physico-chemical properties of bioactive hydroxyapatite derived from caprine bone bio-waste
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Ashish B. Deoghare, Apurba Das, Sushovan Chatterjee, Emon Barua, Sumit Das Lala, Dobbidi Pamu, and Payel Deb
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010302 applied physics ,Materials science ,Process Chemistry and Technology ,Thermal decomposition ,02 engineering and technology ,Thermal treatment ,021001 nanoscience & nanotechnology ,01 natural sciences ,Apatite ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Crystallinity ,Chemical engineering ,law ,visual_art ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,visual_art.visual_art_medium ,Relative density ,Calcination ,Crystallite ,0210 nano-technology ,Thermal analysis - Abstract
This study reports the extraction of bioactive hydroxyapatite (HA) from caprine bone bio-waste using thermal decomposition technique. The role of thermal treatment of the bones (calcined at 700-1300 °C) on the chemical and physico-chemical properties of the derived HA has been investigated. The change in properties of the calcined bone specimens are compared with the raw bones. A highest of 59.8% yield is obtained for the bones calcined at 700 °C which decreases with an increase in calcination temperature. Raman spectroscopy shows that the ionic group in all the ceramic residues corresponds to HA and trace amounts of β-TCP and α-TCP. XRD results confirm the phase stability of HA up to 900 °C beyond which, HA partially decomposes into β-TCP and α-TCP. The crystallite size and crystallinity initially enhances to a maximum of 39.7 nm and 93.1%, respectively with an increase in calcination temperature up to 900 °C. Later, it decreases with a further rise in the temperature. Thermal analysis shows a three-step degradation process of the raw bones. The morphology observed from the FESEM micrographs is found to be porous. Porosity decreases and the grain size increases with an increase in the calcination temperature. A high Ca/P ratio is confirmed from EDS analysis which decreases with a rise in calcination temperature. FETEM micrographs reveal polycrystalline HA particles of size 1.23 × 0.95 μm. Enhancement in relative density and shrinkage is observed with a rise in calcination temperature. In vitro bioactivity test by SBF immersion for 7, 14, 21 and 28 days and test for weight loss for 3, 5, 7, 14, 21 and 28 days show the formation of an apatite layer and biodegradability of HA9 sample, respectively. The study concludes that caprine bones calcined at 900 °C yields bioactive and biodegradable HA with the most optimum properties suitable for tissue engineering applications. more...
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- 2019
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7. Thickness-dependent microwave dielectric and nonlinear optical properties of Bi0.5Na0.5TiO3 thin films
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Alika Khare, Srinivas Pattipaka, Dobbidi Pamu, Gyan Prakash Bharti, K. C. James Raju, and Andrews Joseph
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Materials science ,business.industry ,Band gap ,Physics::Optics ,General Physics and Astronomy ,02 engineering and technology ,Surfaces and Interfaces ,General Chemistry ,Dielectric ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Space charge ,0104 chemical sciences ,Surfaces, Coatings and Films ,Pulsed laser deposition ,Condensed Matter::Materials Science ,Optoelectronics ,Crystallite ,Thin film ,0210 nano-technology ,business ,Refractive index ,Microwave - Abstract
Lead-free Bi0.5Na0.5TiO3 (BNT) films were grown on Pt(111)/Ti/SiO2/Si and quartz substrates for various thickness by using pulsed laser deposition technique. The impact of thickness on structural, microstructural, Raman-spectroscopy, microwave dielectric and nonlinear optical properties have been investigated in detail. X-ray diffraction pattern of BNT films deposited at 700 °C showed rhombohedral crystal symmetry with a small secondary phase of Bi4Ti3O12 and also revealed that the lattice parameters, lattice volume, strain and crystallite size were enhanced with film thickness. The film thickness, refractive index and optical bandgap have been determined by Swanepoel's envelope method and Tauc relation and are in the range of 208 nm–1300 nm, 3.79 eV–3.28 eV and 2.41–1.80, respectively. The third order nonlinear optical properties of films were estimated by Z-scan technique and the 208 nm film exhibited strong nonlinear refractive index (n2 = 4.62 × 10−6 cm2/W) and nonlinear absorption coefficient (β = 0.796 cm/W). The enhancement in microwave dielectric properties was observed with film thicknesses which were measured by using SPDR technique. The leakage current density exhibited the space charge limited current conduction behavior. The enhanced microwave dielectric and nonlinear optical properties of BNT films are promising for microwave tunable and nonlinear photonic device applications. more...
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- 2019
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8. A comprehensive review on electrical properties of hydroxyapatite based ceramic composites
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Dobbidi Pamu and Apurba Das
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Ceramics ,Materials science ,Biomaterial ,Biocompatible Materials ,Bioengineering ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Biocompatible material ,01 natural sciences ,0104 chemical sciences ,Biomaterials ,Durapatite ,Mechanics of Materials ,Biological significance ,Dielectric Spectroscopy ,visual_art ,Physical phenomena ,visual_art.visual_art_medium ,Ceramic ,Electronics ,Composite material ,0210 nano-technology - Abstract
Hydroxyapatite (Ca10(PO4)6(OH)2, HAP1) an immensely favoured biomaterial in the medical industry, is known for its extensive applications in orthopaedics and dentistry because of its bioactivity and osteoconductivity. Apart from bearing chemical resemblance to the inorganic content of bone, HAp exhibit piezoelectric and pyroelectric properties, that assist in responding to mechanical stress similar to bones which aid in speeding up the healing process of large defects in fractured bones. In the recent past, extensive impetus was put in for a systematic investigation of the electrical properties for considering its applicability in bio-electronic devices. Many interesting properties have rolled out from the ongoing researches which have been discussed at length in the article. In reviewing the electrical properties, substantial emphasis was laid on the biological significance of such properties, which is the focal point behind such explorations. An attempt has also been made to review critical issues like addition of suitable composites to HAp for optimized response to various external stimulus. Such areas are hot spots of further research for a comprehensive understanding of the underlying physical phenomena. It is expected that the understanding the electrical properties would play a deciding role in developing HAp based biocompatible electronics, bio sensing and MEMS2.. more...
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- 2019
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9. Low temperature synthesis and characterization of nano‐crystalline Mg(Zr 0.05 Ti 0.95 )O 3 ceramics
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Laishram Robindro Singh, Pallabi Gogoi, and Dobbidi Pamu
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010302 applied physics ,Materials science ,Sintering ,Nanoparticle ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Characterization (materials science) ,Thermal conductivity ,Chemical engineering ,visual_art ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,visual_art.visual_art_medium ,Ceramic ,0210 nano-technology ,Spectroscopy ,Nano crystalline - Published
- 2018
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10. Comparison of solid state synthesis of zinc calcium phosphorous oxide (ZCAP) ceramics under conventional and microwave heating methods
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Dobbidi Pamu, K. Dharmalingam, and R. Anandalakshmi
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Materials science ,Oxide ,Mineralogy ,chemistry.chemical_element ,02 engineering and technology ,Thermal treatment ,Zinc ,010402 general chemistry ,01 natural sciences ,law.invention ,chemistry.chemical_compound ,law ,General Materials Science ,Calcination ,Ceramic ,Fourier transform infrared spectroscopy ,Mechanical Engineering ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,chemistry ,Mechanics of Materials ,visual_art ,visual_art.visual_art_medium ,Carbonate ,0210 nano-technology ,Microwave ,Nuclear chemistry - Abstract
In this study, a weight ratio of 50:30:20 of ZnO:CaO:P2O5 was calcined using microwave and conventional thermal treatment at 800 °C to synthesize zinc oxide calcium phosphorous oxide (ZCAP) ceramics. X-ray diffraction data indicated that microwave synthesized ZCAP ceramics was less crystalline than conventionally synthesized ZCAP. Micro-Raman spectroscopy and FTIR confirmed the presence of ZnO, phosphate and carbonate groups in both heat treatment methods. The reported TGA-DSC results demonstrated that carbonate amount was very less (approx. 0.1%) in microwave synthesized ZCAP while in comparison to carbonate amount was high (approx. 0.69%) in conventionally prepared ZCAP. FESEM image analysis showed that particle sizes were comparatively smaller for microwave synthesized ZCAP than conventionally synthesized ZCAP. Hence, microwave calcinations of ZnO, CaO and P2O5 is a promising method to synthesize ZCAP ceramics compared to conventional thermal calcination treatment. more...
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- 2018
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11. Effects of high-energy ion-beam irradiation on structural and optical properties of (Mg0.95Co0.05)TiO3 thin films
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Dobbidi Pamu, Anand P. Pathak, Mahendra Singh Rathore, T. Santhosh Kumar, N. Srinivasa Rao, Fouran Singh, and Arun Vinod
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inorganic chemicals ,Nuclear and High Energy Physics ,High energy ,Materials science ,genetic structures ,Band gap ,02 engineering and technology ,01 natural sciences ,Ion beam irradiation ,Magnesium titanate ,0103 physical sciences ,General Materials Science ,Irradiation ,Thin film ,Quartz ,010302 applied physics ,Radiation ,business.industry ,technology, industry, and agriculture ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,eye diseases ,Optoelectronics ,sense organs ,0210 nano-technology ,business - Abstract
We report the structural and optical properties of high-energy ion-beam irradiated Co-doped magnesium titanate thin films. (Mg0.95Co0.05)TiO3 (MCT) thin films were deposited on quartz substrates us... more...
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- 2018
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12. Evolution of structural transition, grain growth inhibition and collinear antiferromagnetism in (Bi1-Sm )FeO3 (x = 0 to 0.3) and their effects on dielectric and magnetic properties
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S. Ravi, Dobbidi Pamu, and Bipul Deka
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010302 applied physics ,Materials science ,Condensed matter physics ,Process Chemistry and Technology ,Exchange interaction ,Relaxation (NMR) ,02 engineering and technology ,Dielectric ,021001 nanoscience & nanotechnology ,Polaron ,01 natural sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Materials Science ,Exchange bias ,Ferromagnetism ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Grain boundary ,0210 nano-technology - Abstract
Structural phase transition from rhombohedral (space group : R 3 c ) to orthorhombic (space group: Pnma ) cell is observed in Bi 1- x Sm x FeO 3 ( x = 0 – 0.3) compounds. The evolution of non-ferroelectric Pnma phase reduces the dielectric strength and stabilizes the collinear antiferromagnetism. Temperature variations of dielectric permittivity and its loss component show the presence of Polomska transition and it is found to shift downward towards room temperature with increase in Sm concentration. The frequency dispersion of complex dielectric permittivity was best explained in terms of Havriliak-Negami equation and by invoking the conductivity contribution. The Cole-Cole plots of complex dielectric permittivity show two distinct semicircular arcs corresponding to dielectric relaxation due to grains and grain boundaries respectively. The relaxation dynamics is explained in terms of polaron hopping across Fe 2+ and Fe 3+ sites in grains and short range movement of oxygen vacancies at grain boundaries. The composition dependence of magnetization is explained in terms of evolution of weak ferromagnetism due to partial breaking of spiral spin structure and the growth of collinear antiferromagnetism driven by Pnma phase. We have also observed the exchange bias behavior in some of Sm substituted samples due to the exchange interaction at the interface of coexisting weak ferromagnetic ( R 3 c ) and collinear antiferromagnetic ( Pnma ) phases. more...
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- 2017
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13. Ultrasound-assisted synthesis of poly(MMA–co–BA)/ZnO nanocomposites with enhanced physical properties
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Sachin Sharma, Maneesh Kumar Poddar, Vijayanand S. Moholkar, Dobbidi Pamu, and Srinivas Pattipaka
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chemistry.chemical_classification ,Nanocomposite ,Materials science ,Acoustics and Ultrasonics ,Butyl acrylate ,Organic Chemistry ,Emulsion polymerization ,02 engineering and technology ,Polymer ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Copolymer ,Chemical Engineering (miscellaneous) ,Environmental Chemistry ,Radiology, Nuclear Medicine and imaging ,Thermal stability ,Methyl methacrylate ,0210 nano-technology ,Glass transition - Abstract
The present study reports synthesis and characterization of poly(MMA-co-BA)/ZnO nanocomposites using ultrasound-assisted in-situ emulsion polymerization. Methyl methacrylate (MMA) was copolymerized with butyl acrylate (BA), for enhanced ductility of copolymer matrix, in presence of nanoscale ZnO particles. Ultrasound generated strong micro-turbulence in reaction mixture, which resulted in higher encapsulation and uniform dispersion of ZnO (in native form - without surface modification) in polymer matrix, as compared to mechanical stirring. The nanocomposites were characterized for physical properties and structural morphology using standard techniques such as XRD, FTIR, particle size analysis, UV-Visible spectroscopy, electrical conductivity, TGA, DSC, FE-SEM and TEM. Copolymerization of MMA and BA (in presence of ZnO) followed second order kinetics. Thermal stability (T10%=324.9°C) and glass transition temperature (Tg=67.8°C) of poly(MMA-co-BA)/ZnO nanocomposites showed significant enhancement (35.1°C for 1wt% ZnO and 15.7°C for 4wt% ZnO, respectively), as compared to pristine poly(MMA-co-BA). poly(MMA-co-BA)/ZnO (5wt%) nanocomposites possessed the highest electrical conductivity of 0.192μS/cm and peak UV absorptivity of 0.55 at 372nm. Solution rheological study of nanocomposites revealed enhancement in viscosity with increasing ZnO loading. Maximum viscosity of 0.01Pa-s was obtained for 5wt% ZnO loading. more...
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- 2017
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14. Effect of V2O5 on BaWO4 thin films deposited by RF sputtering for microwave decorative and dielectric capacitor applications
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C. Anil Kumar and Dobbidi Pamu
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010302 applied physics ,Materials science ,business.industry ,02 engineering and technology ,Dielectric ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,law.invention ,Capacitor ,Sputtering ,law ,0103 physical sciences ,Optoelectronics ,Thin film ,0210 nano-technology ,business ,Microwave - Published
- 2017
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15. Structural, dielectric and AC-conductivity studies of Gd doped lead-free Bi0.5Na0.5TiO3 ceramics
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Dobbidi Pamu, Mahesh Peddigari, and Srinivas Pattipaka
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010302 applied physics ,Materials science ,Dc conductivity ,Doping ,02 engineering and technology ,Dielectric ,Conductivity ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Solid state reaction method ,symbols.namesake ,visual_art ,0103 physical sciences ,visual_art.visual_art_medium ,symbols ,Ceramic ,Composite material ,0210 nano-technology ,Raman spectroscopy - Abstract
Lead–free (Bi1-xGdx)0.5Na0.5TiO3 (BGNT; x = 0.00 to 0.06) ceramics synthesized by a solid state reaction method. The effect of Gd on the structural, microstructural and dielectric properties of BNT... more...
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- 2017
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16. Impedance spectroscopy and ac conductivity mechanism in Sm doped Yttrium Iron Garnet
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Bipul Deka, Dobbidi Pamu, S. Ravi, and Aakansha
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010302 applied physics ,Materials science ,Condensed matter physics ,Process Chemistry and Technology ,Transition temperature ,Yttrium iron garnet ,02 engineering and technology ,Conductivity ,021001 nanoscience & nanotechnology ,Polaron ,01 natural sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Dielectric spectroscopy ,chemistry.chemical_compound ,Lattice constant ,chemistry ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Relaxation (physics) ,Grain boundary ,0210 nano-technology - Abstract
Polycrystalline samples of Y 3- x Sm x Fe 5 O 12 for x =0.0 to 3.0 were prepared in single phase form with cubic structure. The analysis of XRD patterns using Reitveld refinement reveals that these samples crystallize in cubic structure with Ia 3 d space group and lattice constant increases systematically with Sm concentration. The depressed and asymmetric semicircle of complex impedance spectra suggests that the relaxation of charge carriers is of non-Debye type and it is controlled by thermally activated charge carriers. Both grains and grain boundaries are found to contribute for the measured complex impedance spectrum, however at higher temperature (T ≥ 543 K), the relaxation process is dominated by the grain boundaries. The temperature dependence of relaxation frequency and conductivity exhibit a change of slope in the vicinity of ferrimagnetic transition temperature which is attributed to the magneto-electric coupling. The analysis of ac conductivity spectra in terms of Jonscher power law suggests that the conduction process is governed by small polaron hopping model for x ≤ 0.5 and for higher concentration overlapping of large polaron tunneling model is found to play a dominant role. The dielectric constant is found to increase with increase with increase in Sm concentration. more...
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- 2017
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17. Liquid phase effect of Bi2O3 additive on densification, microstructure and microwave dielectric properties of Mg2TiO4 ceramics
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Dobbidi Pamu, T. Santhosh Kumar, and R. K. Bhuyan
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010302 applied physics ,Materials science ,Sintering ,02 engineering and technology ,Dielectric ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Microstructure ,01 natural sciences ,Grain size ,Electronic, Optical and Magnetic Materials ,visual_art ,0103 physical sciences ,visual_art.visual_art_medium ,Particle ,Relative density ,Ceramic ,Composite material ,0210 nano-technology ,Microwave - Abstract
Bi2O3 added Mg2TiO4 (MTO) ceramics were prepared by conventional solid-state reaction method. The effect of Bi2O3 on the densification, microstructure and microwave dielectric properties of MTO ceramics was investigated. The Bi2O3 addition significantly lowered the densification temperature of MTO ceramics from 1450°C to 1250°C, which is attributed to the liquid phase effect and smaller initial particle sizes. The dielectric constant (ϵr) was not significantly changed; while the Q × fo was tremendously influenced with Bi2O3 content. A fine combination of microwave dielectric properties (Q × fo = 160,500 GHz, (at 10.48 GHz) and ϵr = 13.2) were obtained for the 1 wt.% Bi2O3 added MTO sample, sintered at 1250°C. Further, the microwave dielectric properties of the MTO ceramics showed significant dependent on relative density, average grain size and oxygen vacancies. more...
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- 2017
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18. Characterization of Zn doped MgTiO3 ceramics: an approach for RF capacitor applications
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Pallabi Gogoi, Dobbidi Pamu, and Laishram Robindro Singh
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010302 applied physics ,Arrhenius equation ,Materials science ,Analytical chemistry ,02 engineering and technology ,Dielectric resonator ,Dielectric ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Microstructure ,01 natural sciences ,Capacitance ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,symbols.namesake ,Capacitor ,law ,0103 physical sciences ,symbols ,Electrical and Electronic Engineering ,0210 nano-technology ,Microwave - Abstract
In the present study the effect of Zn substitution on densification, microstructure, microwave and broad band dielectric properties of MgTiO3 ceramics were investigated. The (Mg1−x Zn x )TiO3 (x = 0.01–0.07) ceramics have been prepared by the conventional solid-state reaction method. The sintering conditions were optimized to obtain the best dielectric properties with maximum relative densities. The microwave dielectric properties are heavily influenced by the amount of x concentration. The optimum dielectric properties of e r ~ 17.34, Q × f o ~ 274 THz, τ f ~ -40.3 ppm/oC is obtained for (Mg0.95Zn0.05)TiO3 ceramics sintered at 1275 °C. The broad band dielectric properties of (Mg0.95Zn0.05)TiO3 ceramics were measured in the frequency range of 1–100 MHz, and temperature range of 133–483 K. Interestingly, the broad band dielectric properties show relaxation behaviour with frequency. The higher temperature dielectric spectrum of (Mg0.95Zn0.05)TiO3 (MZT) ceramics displayed a distinct dispersion, which is shifting towards a lower frequency side. The observed dielectric relaxation behavior is analyzed using Cole–Cole plot. Furthermore, voltage dependent capacitance behavior at different frequencies is studied for the MZT sample, and it’s interesting to note that the capacitance is stable with the variation in voltage. The electrical conductivity study is carried out as a function of frequency and temperature for MZT sample and the activation energy is calculated by using Arrhenius equation, which is found to be 0.07 eV at 10 MHz. The obtained dielectric response of MZT ceramics are suitable for dielectric resonator and type-1 RF capacitor applications. more...
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- 2017
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19. Microwave dielectric and nonlinear optical studies on radio-frequency sputtered Dy2 O3 -doped KNN thin films
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Gyan Prakash Bharti, Alika Khare, Vivek Patel, Mahesh Peddigari, and Dobbidi Pamu
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010302 applied physics ,Materials science ,Band gap ,Analytical chemistry ,Relative permittivity ,02 engineering and technology ,Dielectric ,Sputter deposition ,021001 nanoscience & nanotechnology ,01 natural sciences ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Dissipation factor ,Thin film ,0210 nano-technology ,Refractive index ,Microwave - Abstract
We report the effect of oxygen mixing percentage (OMP) on structural, microstructural, dielectric, linear, and nonlinear optical properties of Dy2O3-doped (K0.5Na0.5)NbO3 thin films. The (K0.5Na0.5)NbO3 + 0.5 wt%Dy2O3 (KNN05D) ferroelectric thin films were deposited on to quartz and Pt/Ti/SiO2/Si substrates by RF magnetron sputtering. An increase in the refractive index from 2.08 to 2.21 and a decrease in the optical bandgap from 4.30 to 4.28 eV indicate the improvement in crystallinity, which is also confirmed from Raman studies. A high relative permittivity (er=281-332) and low loss tangent (tanδ=1.2%-1.9%) were obtained for the films deposited in 100% OMP, measured at microwave frequencies (5-15 GHz). The leakage current of the films found to be as low as 9.90×10−9 A/cm2 at 150 kV/cm and Poole-Frenkel emission is the dominant conduction mechanism in the films. The third order nonlinear optical properties of the KNN05D films were investigated using modified single beam z-scan method. The third order nonlinear susceptibility (ǀχ(3)ǀ) values of KNN05D films increased from 0.69×10−3 esu to 1.40×10−3 esu with an increase in OMP. The larger and positive nonlinear refractive index n2=7.04×10−6 cm2/W, and nonlinear absorption coefficient β=1.70 cm/W were obtained for the 100% OMP film, indicating that KNN05D films are good candidates for the applications in nonlinear photonics and high-frequency devices. more...
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- 2017
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20. Ion beam-induced modification of structural and optical properties of MgTiO3nanocrystalline thin films
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Dobbidi Pamu, Anand P. Pathak, Arun Vinod, Mahendra Singh Rathore, N. Srinivasa Rao, and T. Santhosh Kumar
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010302 applied physics ,Nuclear and High Energy Physics ,Radiation ,Materials science ,genetic structures ,Ion beam ,Analytical chemistry ,02 engineering and technology ,Substrate (electronics) ,Sputter deposition ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,eye diseases ,Swift heavy ion ,Carbon film ,Sputtering ,0103 physical sciences ,General Materials Science ,sense organs ,Irradiation ,Thin film ,0210 nano-technology - Abstract
MgTiO3 thin films were deposited on an amorphous silicon dioxide substrate by the RF magnetron sputtering method by varying the argon and oxygen mixing percentage. These pristine thin films were subjected to thermal annealing at a temperature of 700°C and subsequently two sets of crystalline thin films were irradiated using 100 MeV Au8+ ions at a fixed fluence of 2 × 1013 ions/cm2. XRD spectra reveal that the crystallite size reduces from 21 to 15 nm and crystallinity also decreases drastically after irradiation. AFM images show significant variation in the surface morphology upon irradiation. Optical studies suggest that the band gap as well as the refractive index are both reduced due to SHI irradiation. Ion beam induced modification of the structural, morphological and optical properties of MgTiO3 thin films and the possible mechanisms responsible for variation of the properties of MgTiO3 due to swift heavy ion beam irradiation have been discussed in detail. more...
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- 2017
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21. Size and strain induced phase formation and ferromagnetism in reduced TiO2 powders
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Aneeta Manjari Padhan, Jagadish Kumar, Bhagaban Kisan, Dobbidi Pamu, and Perumal Alagarsamy
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Anatase ,Materials science ,Condensed matter physics ,Spintronics ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Nanocrystalline material ,0104 chemical sciences ,Condensed Matter::Materials Science ,Paramagnetism ,Ferromagnetism ,Phase (matter) ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Density functional theory ,Crystallite ,0210 nano-technology - Abstract
We investigate the strain evolution, phase formation and ferromagnetism of nanocrystalline TiO2 powders prepared by high energy planetary ball milling technique. Pure TiO2 shows the anatase phases in the structural analysis and more than 0.25 h of milled powder turns into Rutile and Magneli phases. The crystallite size and strain were calculated from the X-ray diffraction pattern using the Williamson-Hall equation and the uniform deformation energy density model. Pure TiO2 exhibits paramagnetic nature, which transforms into ferromagnetic one with a moderate moment 0.15 emu/g for 60 h milled powders at an applied field of 12 kOe. The Micro-Raman analyses show the presence of Magneli phase (Ti3O5) along with a shift in the active Eg(1) band for milled powders. X-ray photoelectron spectroscopy results show an oxygen-deficiency peak at 457.7 eV in milled powders. The electron paramagnetic resonance study shows the evidence of oxygen-deficiency which is clear from the resonance signal at 338 mT in milled powders. Further, the electronic structures are investigated by the spin-polarized plane-wave self-consistent field calculation based on density functional theory (DFT) with generalized gradient approximation (GGA) and Hubbard U corrections. The elastic properties are also calculated for pure, oxygen vacancies TiO2 and pure Magneli phase (Ti3O5) crystal. Our results demonstrate the effects of size and strain engineering on the formation of the Magneli phase due to defect induced oxygen vacancy and show the ferromagnetism in TiO2 nanoparticles, which are important for spintronics and other potential applications. more...
- Published
- 2021
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22. Effect of Mn doping on magnetic and dielectric properties of YFeO 3
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S. Ravi, A. Perumal, Bipul Deka, and Dobbidi Pamu
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010302 applied physics ,Materials science ,Condensed matter physics ,Process Chemistry and Technology ,Transition temperature ,Relaxation (NMR) ,02 engineering and technology ,Dielectric ,021001 nanoscience & nanotechnology ,01 natural sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Magnetization ,Magnetic anisotropy ,Superexchange ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology ,Néel temperature ,Spin canting - Abstract
We report the magnetic and dielectric properties of single phase samples of orthorhombic YFe1−xMnxO3 (x=0.0–0.3). The Neel temperature is found to decrease from 646 K for x=0–428 K for x=0.3 due to the weakening of superexchange interaction upon Mn3+ substitution. In addition, Mn substitution induces spin re-orientation transition and the spin re-orientation transition temperature is found to increase from 81 K for x=0.1–295 K for x=0.3. It is explained in terms of significant magnetic anisotropy introduced by the substituted Mn3+ ions. From the analysis of magnetization data exchange field, Dzyaloshinskii-Moriya field and canting angle were estimated and their temperature dependence in the vicinity of spin re-orientation transition temperature is studied. Study of complex impedance spectrum, dielectric constant and ac electrical conductivity in a wide range of frequency (102–106 Hz) across the Neel temperature elucidates the role played by both grains and grain boundaries in shaping the dielectric relaxation. The depressed/asymmetric semicircular shape of Nyquist plots depicts the presence of non-Debye type dielectric relaxation, which is attributed to the short-range movement of oxygen vacancies. The observed increase in dielectric constant and its loss component with increase in Mn concentration is attributed to the leakage current due to hopping of charge carriers between Fe2+ and Fe3+ sites as well as due to the movement of oxygen vacancies. An anomaly in the dielectric constant is observed for all samples in the vicinity of Neel temperature and it is attributed to the disappearance of spin canting induced improper ferroelectric order at the onset of magnetic ordering. The analysis of ac electrical conductivity spectra in terms of Jonscher’s power law suggests that the charge carriers undergo quantum mechanical tunneling between asymmetric double well potential. more...
- Published
- 2017
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23. Microwave dielectric properties of low temperature fired Ba5Nb4O15- BaWO4ceramics supplemented with their own nanoparticles for LTCC applications
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Dobbidi Pamu and Chikkala Anil Kumar
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010302 applied physics ,Marketing ,Materials science ,Composite number ,Sintering ,Nanoparticle ,02 engineering and technology ,Dielectric ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Microstructure ,01 natural sciences ,visual_art ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,visual_art.visual_art_medium ,Relative density ,Ceramic ,Crystallite ,Composite material ,0210 nano-technology - Abstract
Polycrystalline Ba5Nb4O15 (BNO) - BaWO4 (BWO) composite ceramics are prepared by adding their own nanoparticles as a sintering aid. The prepared samples exhibited the maximum relative density of 98.2% at 900°C. The complex dielectric response of these composite ceramics are analysed by Havriliak - Negami (HN) equation. The BNO - BWO composite added with x=3 wt% of their nanoparticles, fired at 900oC displayed the best microwave dielectric properties; er=39 and Q×f0=59.8 THz at 9.44 GHz. The obtained results of BNO - BWO composite makes this material as a potential candidate for LTCC applications. more...
- Published
- 2016
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24. Broadband and Microwave Dielectric Studies on Ba5Nb4O15 Ceramics Supplemented with Its Nanoparticles for Cryogenic Electronic Applications
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Dobbidi Pamu and C. Anil Kumar
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010302 applied physics ,Materials science ,Analytical chemistry ,Nanoparticle ,02 engineering and technology ,Dielectric resonator ,Dielectric ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Microstructure ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Dielectric spectroscopy ,visual_art ,0103 physical sciences ,Materials Chemistry ,visual_art.visual_art_medium ,Ceramic ,Crystallite ,Electrical and Electronic Engineering ,0210 nano-technology - Abstract
Ba5Nb4O15 (BNO) nanopowders were prepared by sol–gel process. The effect of BNO nanopowders (x = 1 wt.%, 2 wt.%, and 3 wt.%) on micron-sized BNO polycrystalline powders were studied systematically. Transmission electron microscope (TEM) images of BNO nanoparticles revealed spherical and cylindrical shapes with average particle sizes of 45 nm and 60 nm, respectively. Further, the dielectric response of BNO ceramics with x wt.% of nanosized particles (x = 1–3) measured in the temperature range of 80°C to 200°C showed relaxation behaviour and is described by using Havriliak–Negami equation. The best microwave dielectric properties of er and Q × f0 values of 39.2 GHz and 59,000 GHz, at 6.52 GHz are obtained for the x = 3 wt.% sample, sintered at 1100°C, and is attributed to maximum density, large and uniform microstructure. The acquired static dielectric response of BNO ceramics with x wt.% of nanosized particles (x = 1–3) are suitable for cryogenic electronic and dielectric resonator applications. more...
- Published
- 2016
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25. Electrical transport and magnetic properties of epitaxial Nd0.7Sr0.3MnO3 thin films on (001)-oriented LaAlO3 substrate
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Dobbidi Pamu, S. Ravi, and T. R. Gopalarao
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Materials science ,Condensed matter physics ,Scattering ,02 engineering and technology ,Substrate (electronics) ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Epitaxy ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,Nuclear magnetic resonance ,Ferromagnetism ,Sputtering ,Electrical resistivity and conductivity ,0103 physical sciences ,symbols ,Thin film ,010306 general physics ,0210 nano-technology ,Raman spectroscopy - Abstract
Nd 0.7 Sr 0.3 MnO 3 thin films were deposited using RF-magnetron sputtering on (001) oriented LaAlO 3 substrate by varying thickness in the range of 12–200 nm. X-ray diffraction patterns of both air annealed and oxygen annealed films show epitaxial growth along (00l) orientation with decrease in lattice strain with increase in film thickness. Raman spectra show the presence of strong peaks corresponding to rotational and stretching modes of MnO 6 octahedra and their intensity is found to decrease with increase in film thickness. Both air and oxygen annealed films except for 12 nm thickness exhibit ferromagnetic transition with a maximum T C of 200 K. The magnetic anisotropic constant was estimated from the analysis of M – H curve and its value is found to decrease with increase in film thickness. Metal-insulator transitions have been observed in all films including the 12 nm thick film. The electrical resistivity data in the metallic region, i.e. close to T MI , were analysed by considering electron–magnon scattering mechanism and in the low temperature region far below T MI ; the analysis was carried out by considering the combination of electron–electron scattering and charge localisation effect. The resistivity data in the insulating region ( T > T MI ) were analysed by considering Mott-variable range hopping model. more...
- Published
- 2016
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26. Effect of Film Thickness in Electrical Resistivity and Magnetic Properties of Nd0.7Sr0.3MnO3 Thin Films
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S. Ravi, T. R. Gopalarao, and Dobbidi Pamu
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010302 applied physics ,Materials science ,Condensed matter physics ,Transition temperature ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Variable-range hopping ,Electronic, Optical and Magnetic Materials ,Lattice constant ,Nuclear magnetic resonance ,Ferromagnetism ,Sputtering ,Electrical resistivity and conductivity ,0103 physical sciences ,Thin film ,0210 nano-technology ,Saturation (magnetic) - Abstract
Nd0.7Sr0.3MnO3 thin films of different thicknesses were deposited on (001)-MgO substrate by using a radio frequency-magnetron sputtering system. These films were divided into two batches and were post-annealed separately in an air and oxygen environment, respectively, at 700 °C. Analysis of X-ray diffraction patterns shows that these films crystallise in cubic structure with a typical lattice constant a = 3.847 Ȧ and it expands with increase in film thickness. Both air- and oxygen-annealed films exhibit ferromagnetic transition and the transition temperature gradually rises as the film thickness is increased. Magnetisation loops recorded at 50 K show that all the prepared thin films show ferromagnetic behaviour with a maximum saturation magnetisation value (3.6 μ B ) comparable to that of bulk sample. The anisotropy constant (K) estimated from the analysis of initial magnetisation curve is found to decrease with increase in film thickness. Metal-insulator transition has been observed and the resistivity data in the insulating region were analysed based on variable range hopping model. more...
- Published
- 2016
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27. Microwave and broadband dielectric properties of Ni substituted MgTiO3 ceramics
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Dobbidi Pamu, Pramod K. Sharma, and Pallabi Gogoi
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010302 applied physics ,Arrhenius equation ,Materials science ,Doping ,Analytical chemistry ,02 engineering and technology ,Dielectric ,Conductivity ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Microstructure ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,visual_art ,0103 physical sciences ,visual_art.visual_art_medium ,symbols ,Relative density ,Ceramic ,Electrical and Electronic Engineering ,0210 nano-technology ,Microwave - Abstract
The present study reports the temperature dependence of dielectric response of Ni doped MgTiO3 ceramics over a broad frequency range. (Mg1−x Ni x )TiO3 (x = 0.00–0.07) ceramics are prepared by a solid-state reaction process. The processing parameters are optimized to achieve maximum relative density. Among all the samples, (Mg0.95Ni0.05)TiO3 (MNTO) ceramics is exhibited the highest density with the best microstructure at 1300 °C. The optimum microwave dielectric properties (e r ~ 17.44, Q × f 0 ~ 181 THz) are displayed by the sample doped with x = 0.05 wt%. The detailed dielectric studies are performed on (Mg0.95Ni0.05)TiO3 composition in two different frequency ranges, 100 Hz–100 kHz at 298–358 K and 1–100 MHz at 133–503 K, respectively. A dielectric constant of 18.26 at 100 MHz is observed for (Mg0.95Ni0.05)TiO3 specimen at temperature 503 K. The frequency dependent conductivity is explained based on the basis of Jonscher power law. Further, the DC conductivity results obey the Arrhenius law, and the obtained activation energies are found to be 0.41 and 0.06 eV for (Mg0.95Ni0.05)TiO3 ceramics, measured at 100 MHz for high temperature (293–503 K) and cryogenic temperatures (133–293 K), respectively. more...
- Published
- 2016
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28. Dielectric and Optical Characterization of RF Sputtered Ba5Nb4O15–BaWO4 Composite Films for Electronic and Smart Window Applications
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Dobbidi Pamu and C. Anil Kumar
- Subjects
010302 applied physics ,Nanocomposite ,Materials science ,business.industry ,02 engineering and technology ,Dielectric resonator ,Dielectric ,Sputter deposition ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Optics ,Electrochromism ,0103 physical sciences ,Materials Chemistry ,Transmittance ,Optoelectronics ,Electrical and Electronic Engineering ,Thin film ,0210 nano-technology ,business ,Diffractometer - Abstract
We demonstrate the deposition of Ba5Nb4O15–BaWO4 (BNO–BWO) composite thin films by radio frequency (RF) magnetron sputtering under different oxygen mixing percentages (OMP). Significantly, the x-ray diffractometer revealed the coexistence of both BNO hexagonal perovskite structure with BWO scheelite structure. The microstructures of the composite films reveal two types of grains: BNO exhibited small rod-shaped grains, whereas the BWO showed large hexagonal grains, and the chemical compositions of these grains are confirmed using energy dispersive spectroscopy analysis. The optical transmittance of the as-deposited films show the transmittance above 90% and after annealing they exhibit pale yellow color, and this response may be due to the electrochromic response of these films. The refractive index of the films decreases for the films deposited above 25% OMP, whereas the optical bandgap increases with an increase in OMP. The dielectric response of Ag/BNO–BWO Pt/Ti/SiO2/Si thin film capacitors showed that the obtained dielectric properties are independent of measured frequency and temperature. The split-post dielectric resonator method was used to measure dielectric properties at discrete microwave frequencies (5, 10, and 15 GHz) and are in the range of e r = 22.47–49.81 and tanδ = 0.0038–0.0010, for annealed films. The activation energies of the composite films obtained from the Arrhenius relation are in the range of 0.021–0.008 eV. BNO–BWO nanocomposite films find applications in integrated electronic devices, smart windows, and information display applications. more...
- Published
- 2016
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- View/download PDF
29. Deposition of biphasic calcium phosphate film on laser surface textured Ti–6Al–4V and its effect on different biological properties for orthopedic applications
- Author
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Rasmi Ranjan Behera, Apurba Das, Dobbidi Pamu, Abshar Hasan, Mamilla Ravi Sankar, and Lalit M. Pandey
- Subjects
Materials science ,Mechanical Engineering ,Metals and Alloys ,02 engineering and technology ,Surface finish ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Contact angle ,Chemical engineering ,Coating ,Mechanics of Materials ,Superhydrophilicity ,Materials Chemistry ,Surface roughness ,engineering ,Texture (crystalline) ,Wetting ,0210 nano-technology ,Protein adsorption - Abstract
The present study reports laser surface texturing (LST) of Ti–6Al–4V using a Nd-YAG laser with a particular set of parameters and three different overlapping factors (OF): 0%, 25% and 50%. Biphasic calcium phosphate (BCP) film was deposited on bare as well as textured Ti–6Al–4V specimens by using radio frequency (RF) sputtering. The simultaneous effect of texturing as well as BCP coating on different physical and biological properties was investigated. The study revealed that the surface wettability of bare Ti–6Al–4V enhanced after laser texturing (as contact angle reduced from 89° to 71°-77°). It was further improved upon BCP deposition to make the Ti–6Al–4V superhydrophilic (contact angle ≈ 17°-21°). It was also observed that the surface roughness of bare Ti–6Al–4V significantly increased from Ra ≈ 94 nm to Ra ≈ 0.98–1.84 μm for different micro-dimpled texture substrates. The dimensions of micro-dimpled texture did not change after BCP deposition; however, a non-uniform film is deposited with increase in surface roughness. Protein adsorption was found as a function of surface hydrophobicity, which increased from 5.3 to 7.11 μg/cm2 with the rise in hydrophobicity of modified surfaces. Compared to bare Ti–6Al–4V and BCP deposited bare-Ti-6Al–4V surfaces, the BCP deposited textured surfaces exhibit higher number of well spread MG63 osteoblast cells. For the same surface chemistry, increase in surface area (roughness) improves cellular behavior. With texturing of the substrate, the cell adhered percentage and average cell area improved significantly and BCP-(50% OF)–Ti–6Al–4V was found to have the maximum cell spreading and proliferation. Overall, these findings revealed that a micro-dimpled textured surface followed by BCP film deposition strategy improved the physio-chemical properties of surfaces such as surface roughness and wettability. This in turn enhanced the bioactivity, cell adhesion and proliferation of bone cells (MG63) on modified Ti–6Al–4V surfaces and based on the results we envisage that can be potentially used for orthopedic and dental applications. more...
- Published
- 2020
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30. Effect of TiO2 addition on adhesion and biological behavior of BCP-TiO2 composite films deposited by magnetron sputtering
- Author
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Dobbidi Pamu, Lalit M. Pandey, Rasmi Ranjan Behera, Abshar Hasan, Mamilla Ravi Sankar, and Apurba Das
- Subjects
Materials science ,Annealing (metallurgy) ,Simulated body fluid ,Composite number ,Bioengineering ,02 engineering and technology ,Sputter deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Apatite ,0104 chemical sciences ,Biomaterials ,Crystallinity ,Adsorption ,Chemical engineering ,Mechanics of Materials ,visual_art ,visual_art.visual_art_medium ,Wetting ,0210 nano-technology - Abstract
The present investigation focuses on the deposition of biphasic calcium phosphate (BCP) and titania (TiO2) composite films on Ti-6Al-4V substrates using radio frequency (RF) magnetron sputtering. Three different compositions such as 100% BCP, 25% TiO2-75% BCP and 50% TiO2-50% BCP films were fabricated, and the physical, mechanical and biological behaviors of the films were analyzed. Post deposition, the films were annealed at 700 °C for 2 h to induce the crystallinity and to study its effect on different properties. The wettability was found to be 95°(±3°) for 100% BCP, 73°(±2°) for 25% TiO2-75% BCP and 35°(±1°) for 50% TiO2-50% BCP films, indicating improvement in wettability with an increase of TiO2 weight percent in the composite films. The value of critical load (Lc2) for 100 BCP film improved from 8.7 N to 14.8 N (25 TiO2-BCP) and >19 N (50 TiO2-BCP film), indicating improvement in bonding strength with TiO2 addition. The fetal bovine serum (FBS) adsorption decreased from 7.11 ± 0.25 to 4.42 ± 0.17 μg/cm2 with TiO2 weight percent from 0 to 50%. Cell adhesion and proliferation significantly improved in 100% BCP, 25% TiO2-75% BCP and 50% TiO2-50% BCP films as compared to uncoated Ti-6Al-4V. The maximum cell proliferation was found on the surface of 50% TiO2-50% BCP film (210.1 ± 6.5%) after 6 days of incubation. However, after annealing all the films exhibited less cell adhesion and cytocompatibility presumably due to change in composition. Globular apatite structure was observed on all modified surfaces after 7 days immersion in simulated body fluid (SBF); however, the growth rate was higher for 50 TiO2-BCP films. All these results revealed that the addition of TiO2 in BCP film (without annealing) is advantageous for improving the bonding strength as well as the bioactivity of implants, which can be used for long-term dental and orthopedic applications. more...
- Published
- 2020
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31. Degradation kinetics and surface properties of bioceramic hydroxyapatite coated AZ31 magnesium alloys for biomedical applications
- Author
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Ashutosh Kumar, Apurba Das, Lalit M. Pandey, V.S. Yadav, Mamilla Ravi Sankar, and Dobbidi Pamu
- Subjects
Materials science ,Biocompatibility ,Magnesium ,Mechanical Engineering ,Simulated body fluid ,chemistry.chemical_element ,02 engineering and technology ,Bioceramic ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Reaction rate constant ,Coating ,Chemical engineering ,chemistry ,Mechanics of Materials ,Sputtering ,engineering ,Degradation (geology) ,General Materials Science ,0210 nano-technology - Abstract
Controlling degradation and improving the biocompatibility of AZ31 magnesium alloys is under continuous research for its practical biomedical applications. Here we have applied a bio-ceramic, hydroxyapatite (HAp), on AZ31 through radio frequency sputtering. The degradation analysis was investigated in SBF (simulated body fluid) for 48 days through weight loss of sample and release of Mg2+ ions by atomic absorption spectroscopy. XRD and elemental analysis confirmed the successful coating of HAp on AZ31. AZ31 was found to be hydrophilic, which became hydrophobic after sputtering. The degradation kinetics was modeled with a single exponential expression and both the weight loss and release of Mg2+ ions data of sample agreed with the same rate constant. The rate of degradation of bare AZ31 was decreased to 20% for the 9 h coated AZ31. more...
- Published
- 2020
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32. Effect of Ar:O2 gas atmosphere on optical properties of Y2O3-doped ZnO thin films by RF sputtering
- Author
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R. Chowdhruy, R. Jayaganthan, Dobbidi Pamu, S. Sasi Florence, Mohammad Haider, Y. Alajlani, M. Sowjanya, and Mohammad Shariq
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Materials science ,Photoluminescence ,Band gap ,Doping ,Analytical chemistry ,General Physics and Astronomy ,Substrate (electronics) ,01 natural sciences ,010305 fluids & plasmas ,Sputtering ,0103 physical sciences ,Transmittance ,Thin film ,010306 general physics ,Wurtzite crystal structure - Abstract
In this work, the radio frequency magnetron sputtering technique (RF sputtering) was utilized for the deposition of Y2O3-doped zinc oxide (ZnO) thin films on a SiO2 substrate. The microstructures and optical properties of the thin films deposited utilizing various gas (Ar:O2) ratios at 400 °C were characterized. XRD investigation of thin films demonstrates that all deposited films are polycrystalline and there is a single phase hexagonal wurtzite type structure with a strong (002) orientation. An increment of O2 in the gas mixture reduces the intensity of peak (002). Y2O3-doped ZnO thin films exhibited denser morphology with refined microstructure as compared to pure ZnO films. The absorbance and transmittance of doped ZnO thin films were measured by UV-VIS-IR spectrophotometer in the wavelength range 300 nm to 800 nm. High transmittance in the visible region and high band gap of films were revealed. Photoluminescence (PL) of films was estimated at the excitation wavelength of 325 nm and it uncovered two PL peaks present in UV and visible regions (400 nm to 445 nm). The effect of Ar:O2 gas proportion on stoichiometry, structural and optical properties of the Y2O3-doped ZnO thin films was also revealed. FullText for HTML: https://doi.org/10.1209/0295-5075/129/34003 more...
- Published
- 2020
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33. Mechano-tribological properties and in vitro bioactivity of biphasic calcium phosphate coating on Ti-6Al-4V
- Author
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Apurba Das, Rasmi Ranjan Behera, Mamilla Ravi Sankar, Dobbidi Pamu, and Lalit M. Pandey
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Calcium Phosphates ,Materials science ,Surface Properties ,Simulated body fluid ,Biomedical Engineering ,02 engineering and technology ,engineering.material ,010402 general chemistry ,01 natural sciences ,Apatite ,Biomaterials ,Contact angle ,Coating ,Coated Materials, Biocompatible ,Sputtering ,Biomimetic Materials ,Hardness ,Alloys ,Mechanical Phenomena ,Titanium ,Sputter deposition ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Body Fluids ,Chemical engineering ,Mechanics of Materials ,visual_art ,engineering ,visual_art.visual_art_medium ,Wetting ,0210 nano-technology ,Layer (electronics) - Abstract
Biphasic calcium phosphate (BCP) consists of hydroxyapatite (HA) and beta-tricalcium phosphate (β-TCP). BCP is mainly used in artificial tooth and bone implants due to higher protein adsorption and osteoinductivity compared to HA alone. Although, many studies have been investigated on radio frequency (RF) magnetron sputtering of HA on Ti and its alloy, however, limited studies are available on BCP coating by this process and its bioactivity and adhesion behavior. Thus, in order to obtain a better understanding and applications of BCP films, RF magnetron sputtering is used to deposit BCP films on Ti-6Al-4V in the present study. The effect of film thickness on wettability, mechanical properties and in vitro bioactivity at a particular set of sputtering parameters are investigated. BCP film thickness of 400 nm, 700 nm and 1000 nm are obtained when sputtered for 4 h, 6 h and 8 h, respectively. Although the phase compositions are almost same for all films, the surface roughness values varies around 112–153 nm with rise in film thickness. This in turn enhances hydrophilicity in accordance to Wenzel relation as the contact angle decreases from 89.6 ± 2° to 61.2 ± 2°. It is found that the 1000 nm film possess highest micro-hardness and surface scratch resistance. No cracking of film up to scratch load of 2.3 N and no significant delamination up to load of 7.8 N are observed, indicating very good adhesion between BCP films and Ti-6Al-4V substrate. There is a great improvement in wt% apatite layer formation on all films when dipped in simulated body fluid (SBF) for 14 days. Among these, 1000 nm sputtered film results the highest increase in wt% apatite layer from 44.87% to 86.7%. The apatite layer possess small globular as well as elliptical structure are nucleated and grew on all the BCP films. Thus, sputtering of BCP films improves wettability, mechanical properties as well as bioactivity of Ti-6Al-4V, which can be applied for orthopedic implants. more...
- Published
- 2018
34. Optical, Dielectric Characterization and Impedance Spectroscopy of Ni-Substituted MgTiO3 Thin Films
- Author
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Pallabi Gogoi, Dobbidi Pamu, Pramod K. Sharma, and P. Srinivas
- Subjects
010302 applied physics ,Materials science ,Analytical chemistry ,02 engineering and technology ,Dielectric ,Sputter deposition ,Conductivity ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Arrhenius plot ,Electronic, Optical and Magnetic Materials ,Dielectric spectroscopy ,Amorphous solid ,0103 physical sciences ,Materials Chemistry ,Dissipation factor ,Electrical and Electronic Engineering ,Thin film ,0210 nano-technology - Abstract
We report the effects of oxygen mixing percentage (OMP) and annealing temperature on surface morphology, optical, dielectric and electrical properties of (Mg0.95Ni0.05)TiO3 (MNT) thin films deposited onto amorphous SiO2 and platinized silicon (Pt/TiO2/SiO2/Si) substrates by radio frequency (RF) magnetron sputtering. The annealed films exhibited the highest refractive index, 2.05, at 600 nm with an optical bandgap value of 4.33 eV. The metal–insulator–metal (MIM) capacitors of the MNT thin films were fabricated under different OMPs and the dielectric properties were analyzed by using Maxwell–Wagner two-layer theory and Koop’s phenomenological theory. MNT films prepared under 50% OMP displayed the highest dielectric constant (11.21) and minimum loss tangent (0.0114) at 1 MHz. The impedance spectroscopy of the films deposited under 50% OMP has been studied. The Nyquist plots of MNT films revealed two semi-circular arcs and is explained on the basis of an equivalent circuit model. The frequency-dependent alternative current (AC) conductivity followed the Jonscher’s power law. The activation energies are calculated using the Arrhenius relationship. The hopping frequency of the charged species was calculated, and the correlation between AC and direct current (DC) conduction mechanisms established in accordance with the Barton–Nakajima–Namikawa (BNN) relationship. more...
- Published
- 2015
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35. Impedance Spectroscopy, Broadband, and Microwave Dielectric Properties of Mechanically Alloyed Ba5Nb4O15Ceramics
- Author
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Chikkala Anil Kumar, Dobbidi Pamu, and Sylvester Josephine
- Subjects
Imagination ,Materials science ,Chemical substance ,Microwave dielectric properties ,media_common.quotation_subject ,Nanotechnology ,02 engineering and technology ,01 natural sciences ,0103 physical sciences ,Broadband ,Materials Chemistry ,Ceramic ,media_common ,010302 applied physics ,Marketing ,Thesaurus (information retrieval) ,business.industry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Dielectric spectroscopy ,visual_art ,Ceramics and Composites ,visual_art.visual_art_medium ,Optoelectronics ,0210 nano-technology ,Science, technology and society ,business - Published
- 2015
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36. Peculiarities of the temperature dependence of electron spin resonance and Raman studies of Zn1−xNixO/NiO two-phase nanocomposites
- Author
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Subhash Thota, Ashok Kumar, Dobbidi Pamu, Antaryami Mohanta, D. C. Joshi, and Sisir Kumar Nayak
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,Phonon ,Magnon ,Non-blocking I/O ,General Physics and Astronomy ,Resonance ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,law.invention ,Condensed Matter::Materials Science ,symbols.namesake ,law ,0103 physical sciences ,symbols ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology ,Raman spectroscopy ,Electron paramagnetic resonance ,Raman scattering ,Wurtzite crystal structure - Abstract
A meticulous investigation of electron-spin-resonance (ESR) and Raman spectroscopy of the two-phase nanocomposites of Zn1−xNixO/NiO is reported. The temperature variation of X-band ESR parameters viz., resonance field HR(T) and line-width ΔHPP(T) follows the power-law variation (δHR = (ΔHPP)n) of Nagata and Ishihara model, which was used to understand the orientation of statistical ensemble of particles with respect to a given direction of the anisotropy axis. This analysis yields the exponent “n” ≃ 2.13 and 2.85 for the composite system Zn1−xNixO/NiO and pure NiO suggesting the presence of partial and randomly oriented ellipsoidal nanocrystallites, respectively. The Raikher and Stepanov model has been employed to probe the role of amorphous Ni3+ clusters on the observed ESR spectra. Interestingly, after Ni substitution, a new zone boundary phonon mode was noticed at 129 cm−1 for all the samples, which is usually forbidden in the first-order Raman scattering for wurtzite ZnO. In addition to the 2M magnon ... more...
- Published
- 2016
- Full Text
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