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Erbium orthochromite, ErCrO3, is a distorted-perovskite which has antiferromagnetic ground state below 10 K while Cr3+ magnetic moments order at 133 K. The temperature dependence of magnetization is studied across different magnetic phases for ErCrO3 and different magnetization isotherms are analyzed. In the presence of external magnetic field, polycrystalline ErCrO3 develops weak ferromagnetism from antiferromagnetic ground state. These magnetic phase transitions are observed to be of first order which is justified by thermal hysteresis and Arrott-plots., Under review in Materials Research Express

Undoped ZnO films were deposited using pulsed laser deposition technique on Si and glass substrates in different O2 partial pressures (ranging from 10−5 mbar to 3 mbar) and substrate temperatures. When the substrate temperature is 500 °C and O2 partial pressure (pp) ∼ 3 mbar, randomly oriented ZnO hexagons were observed on glass substrate, whereas, dense ZnO hexagonal rod like structures (diameter ranging from 200–500 nm) were observed on Si substrate. The photoluminescence (PL) characterization of ZnO film grown on Si exhibited an intense defect free narrow excitonic emission in the UV region (Full width half maximum (FWHM) ∼ 11.26 nm) as compared to broad emission (FWHM ∼ 57.06 nm) from that grown on glass. The parent film emission was found to shift from UV to blue region on doping ZnO with Vanadium.

Polycrystalline and highly preferred (1 0 2?) orientated Bi 0.5Sr0.5FeO3-? thin films were grown by pulsed laser deposition (PLD) on n-Si (2 0 0) and MgO (2 0 0) single crystalline substrates respectively. The thin films were inspected using x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy and atomic force microscopy techniques. The electrical surface-resistivity, dielectric resonance, electric polarization, and magnetic properties of the thin films were studied. At room temperature, depending on deposition conditions, the polycrystalline thin films grown on n-Si substrates were found to exhibit an electrical surface-resistivity of the order of 103106 ?, a piezoelectric resonance in the frequency range of about 2526 MHz, a relaxor-type ferroelectric hysteresis with a maximum polarization of 0.0150.055?Ccm?2 and magnetic hysteresis. Similarly, the thin films grown on MgO substrates exhibited an electrical surface-resistivity of the order of 109 ?, multiple piezoelectric resonances in the frequency range of about 845 MHz, a linear variation of polarization with applied electric field and either a linearly varying magnetization or magnetic hysteresis which depends on the deposition conditions.� 2014 IOP Publishing Ltd Printed in the UK.

Zinc Oxide: The Versatile Material with an Assortment of Physical Properties.- Laser Nano-Soldering of ZnO Nanowires and GaN Thin Film for Fabrication of Hetero p-n Junction.- Photoluminescence Processes in ZnO Thin Films and Quantum Structures.- Effect of Oxygen Pressure on Photoluminescence Spectra and Hall Coefficients of Li-Ni co-doped ZnO Films Grown by a Pulsed Laser Deposition.- Lasing Characteristics of an Optically-pumped Single ZnO Nanocrystal and Nanomachining for Controlling Oscillation Wavelength.- Deposition of Aluminum-doped ZnO Films by ICP Assisted Sputtering.- Control of ZnO Nanocrystals Synthesized by Nanoparticle-assisted Pulsed Laser Deposition using Buffer Layer and Laser Irradiation.- Influence of Sb as a Catalyst in Synthesize of Sb Doped ZnO Nanostructures using NAPLD (Nano Particle Assisted Pulsed Laser Deposition) for UV LED Applications.- Time- and spatially-resolved Luminescence Spectroscopy of ZnO Nanostructures.- Synthesis of Polycrystalline Silicon Carbide (SiC) Thin Film Using Pulsed Laser Deposition.- Preparation and Characterization of ZnO Nanorods, Nanowalls and Nanochains.- Synthesis and Characterization of ZnO-based Phosphors and Related Phosphor Composites in Bulk, Thin Film and Nano Form.- Zinc Oxide Nanomaterials as Amylase Inhibitors and for Water Pollution Control.- Zinc Oxide - from Optoelectronics to Biomaterial: A Short Review.- On the Optical and Magnetic Properties of Doped ZnO.- Low-temperature Photoluminescence of Sb-doped ZnO Nanowires Synthesized on Sb-coated Si Substrate by Chemical Vapor Deposition Method.- Experimental and Theoretical Investigations of Dopant, Defect and Morphology Control on the Magnetic and Optical Properties of Transition Metal Doped ZnO Nanoparticles.

Cross-sectional structural characteristics of the CVD diamond coatings deposited on the tungsten carbide (WC-Co) substrates were analysed using Raman imaging technique. The grain size of the nanocrystalline diamond (NCD) coatings was observed to deviate from the nanocrystallinity with increasing thickness and exhibited the surface characteristics of microcrystalline diamond (MCD). However, thick diamond coatings with surface nanocrystallinity is the key requirement for load-bearing tribological applications. Tribological tests have clearly indicated the significance and need for the top-layer nanocrystallinity. Graded composite diamond coatings with an architecture of NCD/transition-layer/ MCD/WC-Co are potentail candiadates to realize thick diamond coatings with top-layer nanocrystallinity. Residual stresses along the cross-section of the graded composite diamond coatings were analysed using Raman imaging technique, which confirmed the improved interfacial integrity of the graded composite diamond coatings. � 2013 Elsevier B.V.

Zinc oxide has the potential to replace GaN as the next-generation white light emitting diode material. This wide bandgap semiconductor with an excitonic binding energy of ~60 meV has been researched extensively in the last decade due to its immense potentiality for blue/UV light emitting devices. ZnO lattice is amenable to doping with transition metal ions (TM) and 4f-elements. Such a doping activity in ZnO has been mainly aimed at the realization of n and p-type conductivity and room temperature diluted magnetic semiconducting behavior. Several doping studies have been attempted in order to get an insight into the changes in physical properties with the emphasis on fabricating of all ZnO p–n junctions for white light/UV emission. The challenge is to obtain highly stable p-ZnO with doping. Our group has been working on doping studies in ZnO. Ni doping shows a dramatic decrease in resistivity in polycrystalline ZnO. Stable and low resistive p-type conduction in ZnO was not possible with monovalent ion (Li, Ag etc.) doping. Recent work indicated the possibility of inducing shallow holes into ZnO lattice using co-doping route. We used Li and Ni co-doping to realize a low resistive, p-type and magnetic ZnO. Aligned 1-dimensional ZnO nanowires can also be obtained using PLD and other methods. Our research group at IIT Madras has been working closely with Kyushu University and other partner universities in Japan to make research in ZnO a worthwhile attempt aimed at device applications. We will present, in this chapter, overall physical properties of ZnO with our important results related to the doping aspects in ZnO.

The fabrication of p-type ZnO crystal is motivated by the need to develop ZnO semiconductor devices. On the other hand, it is well-known that high-quality nano-sized ZnO crystal can be easily obtained by various crystal growth techniques. Consequently, we tried to grow p-type Sb-doped ZnO nanowires by the chemical vapor deposition under various deposition temperature conditions and investigated their optical properties by photoluminescence (PL) spectroscopy. Multiple emission peaks caused by free excitons, excitons bound to donors and structural defects, and acceptors formed by Sb-doping were observed. The temperature dependence of PL confirmed the existence of acceptor level due to Sb-doping, and the activation energy of the acceptor level was estimated to be 125 meV.

Phosphors are light emitting solids that play an important role in the lighting industry. The physics of doping suitable elements plays an equally important role in controlling the emission properties. The choice of host lattice is the key in controlling the charge transfer mechanism. Zn2SiO4 is a useful host material, and in this chapter we discuss on the effect of doping in various forms of this host material. Zn2SiO4:Mn powder (bulk) phosphors have been synthesized by sol–gel [1] and solid-state method, and thin films grown by pulsed laser deposition [2]. The optimization parameters like growth temperature, vacuum, and oxygen partial pressure (in case of thin films) that determine the luminescent efficiency of the phosphors will be highlighted. The defect and its related emission in ZnO encapsulated SiO2 nanocomposites [3] synthesized using urea assisted sol–gel techniques projecting toward the fabrication of UV-LED pumped white LED will be discussed in detail.

Since the co-doping method is a key technique for the realization of p-type ZnO films, we grew samples by the co-doping of Li and Ni impurities using a pulsed laser deposition technique to investigate the formation of a possible acceptor level. The effect of the oxygen gas pressure on the physical properties is discussed. The electrical and optical properties of the films were investigated through Hall and photoluminescence (PL) measurements. Although p-type conduction was not observed, we were able to observe the change in conduction type from n-type to insulating upon increasing the oxygen pressure. PL spectra of co-doped samples were investigated at 10 K by comparison with those of mono-doped samples. Co-doping drastically changes the PL spectral shape and reveals additional peaks at 2.4 and 3.0 eV, which could not be observed in the spectra of mono-doped samples. The experimental results showed that the acceptor level was indeed formed by the co-doping of Li and Ni.

We report a strong rare-earth size dependence of ${\mathit{T}}_{\mathit{c}}$ in R${\mathrm{Sr}}_{2}$${\mathrm{Cu}}_{2.85}$${\mathrm{Re}}_{0.15}$${\mathrm{O}}_{\mathit{z}}$ (R=rare earth, z\ensuremath{\approxeq}7.2) compounds, unlike in R${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{y}}$ compounds. A strong correlation is observed between the superconducting transition temperature and the orthorhombicity of the structure, which itself is R-size dependent. Orthorhombicity is highest for ${\mathrm{HoSr}}_{2}$${\mathrm{Cu}}_{2.85}$${\mathrm{Re}}_{0.15}$${\mathrm{O}}_{\mathit{z}}$ and ${\mathrm{ErSr}}_{2}$${\mathrm{Cu}}_{2.85}$${\mathrm{Re}}_{0.15}$${\mathrm{O}}_{\mathit{z}}$ compounds, which also have yielded the highest ${\mathit{T}}_{\mathit{c}}$ (\ensuremath{\approxeq}42 K). Significantly, ${\mathrm{TbSr}}_{2}$${\mathrm{Cu}}_{2.85}$${\mathrm{Re}}_{0.15}$${\mathrm{O}}_{\mathit{z}}$ stabilizes in a 1-2-3 structure and also superconducts (${\mathit{T}}_{\mathit{c}}$\ensuremath{\approxeq}22 K), whereas ${\mathrm{EuSr}}_{2}$${\mathrm{Cu}}_{2.85}$${\mathrm{Re}}_{0.15}$${\mathrm{O}}_{\mathit{z}}$ does not superconduct, although it forms a single phase. \textcopyright{} 1996 The American Physical Society.

In this article, we report our recent results on the synthesis of nano-ink and drop-casted films of CuInGaS2 (CIGS), which acts as the absorber material for CIGS-based solar cells. The morphological and optical property changes of CIGS films have been compared to those of nano-CuInS2 (CIS) films deposited on glass substrates. It is found that the microstructure and morphology of these films depend strongly on the presence of Ga. High-resolution transmission electron microscopy reveals that CIGS nanoparticles are 4-5 times larger than CIS nanoparticles. The roughness of CIGS films could be reduced on preheating the drop-casted films prior to sulphurisation. The absorption onset for CIGS is lower than that of CIS due to Ga substitution in place of In. Raman spectra showed a noticeable contribution from Cu-Au mode in CIGS films. Larger nanoparticles in CIGS are attributed to faster growth kinetics due to higher Cu:In ratio than in CIS. � 2013 Copyright Taylor and Francis Group, LLC.

We report on the suppression of FeLi� antisite defects in LiFe(PO 4)1-xF3x with 0 ? x ? 0.4 prepared by sol-gel and hydrothermal methods. Evidence for a systematic suppression of antisite defects upon fluorine doping in LiFePO4 is inferred from Fourier transform infrared spectra, wherein a noticeable red shift in the symmetric P-O stretching vibrational mode of (PO4) 3- polyanion from 970 to 957 cm-1 was observed. We report detailed structural and compositional studies of LiFe(PO4) 1-xF3x, and discuss the implications for the performance of LiFePO4 cathodes in lithium ion batteries.� 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In this work, integrated composite diamond (ICD) coatings have been achieved with top layer nanocrystallinity, low friction coefficient and enhanced integrity. ICD coatings were deposited on chemically treated tungsten carbide (WC-Co) substrates using hot filament chemical vapour deposition technique. Nanocrystalline diamond (NCD) layer was deposited over microcrystalline diamond (MCD) layer with a coating architecture of NCD/transition layer/MCD/WC-Co. Graded transition layer thickness of ? 1 ?m was realized by controlling the process parameters such as methane concentration and chamber pressure in order to integrate the MCD and NCD layers. Integrity of the coatings was examined by the cross-sectional studies. Structural and microstructural characteristics of ICD coatings were compared with those of MCD coatings. The measured average nanohardness of ICD coating was ? 96 GPa. A low and stable friction coefficient of ? 0.06 was observed for ICD coatings against silicon nitride (Si3N4). ICD coatings were anticipated to exploit the advantages of both NCD and MCD coatings and these coatings can be promising candidates for various mechanical applications. � 2012 Elsevier Ltd. All rights reserved.

We demonstrate a tunable bandgap from 2.32 eV to 2.09 eV in phase-pure BiFeO3 by controlling the particle size from 65 nm to 5 nm. Defect states due to oxygen and microstrain show a strong dependence on BiFeO 3 particle size and have a significant effect on the shape of absorbance curves. Oxygen-defect induced microstrain and undercoordinated oxygen on the surface of BiFeO3 nanoparticles are demonstrated via HRTEM and XPS studies. Microstrain in the lattice leads to the reduction in rhombohedral distortion of BiFeO3 for particle sizes below 30 nm. The decrease in band gap with decreasing particle size is attributed to the competing effects of microstrain, oxygen defects, and Coulombic interactions. � 2013 AIP Publishing LLC.

The diamond nanowire (DNW) film was deposited by N2-enriched microwave plasma-enhanced chemical vapour deposition (MPECVD) process. As-deposited DNW film was treated in O2 plasma which resulted in chemical and microstructural modification. Sheath of the DNW film is chemically constituted by amorphous carbon (a-C)- and graphite (sp2C=C)-like bonding. However, nanowires transformed into ultra-small spherical grains after the O2-plasma treatments. In this condition, a-C and sp 2C=C bonding significantly reduced due to plasma etching caused by oxygen atoms. After the O2-plasma treatment, formation of functional groups such as C=O, C-O-C, O-H, O-CH3 and H2O was observed on the surface and inside the wear track as evident from the micro FTIR analysis. H2O is hydrogen bonded to oxygen-containing groups such as -OH and -H. The O2-plasma-exposed DNW film exhibits surface charging and causes formation of dangling bonds and electron trapping centres. This results in significant decrease in contact angle, hence superhydrophilic behaviour. The friction coefficient of O2-plasma-treated film showed super low value ?0.002 with high wear resistance 2 � 10-12 mm3 N-1 m-1. In the reciprocating ball-on-disc tribology test, only ?80 nm wear loss was observed after the 1 km of sliding distance at 10 N loads. Such an advance in tribological properties is explained by passivation of covalent carbon bonding and transformation of sliding surfaces by weak van der Waals and hydrogen bondings. High surface energy and the consequent superhydrophilic behaviour of film is attributed to the formation of the above-mentioned functional groups on the surface. This protects against deformation of the wear track leading to extremely high wear resistance. � 2013 IOP Publishing Ltd.

Ni doped, Li doped and (Li, Ni) codoped ZnO thin films were successfully grown using a pulsed laser deposition technique. Undoped and doped ZnO thin films were investigated using extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge spectroscopy (XANES). Preliminary investigations on the Zn K-edge of the undoped and doped ZnO thin films revealed that doping has not influenced the average Zn-Zn bond length and Debye-Waller factor. This shows that both Ni and Li doping do not appreciably affect the average local environment of Zn. All the doped ZnO thin films exhibited more than 50% of substitutional Ni, with a maximum of 77% for 2% Ni and 2% Li doped ZnO thin film. The contribution of Ni metal to the EXAFS signal clearly reveals the presence of Ni clusters. The Ni-Ni distance in the Ni0 nanoclusters, which are formed in the film, is shorter with respect to the reference Ni metal foil and the Debye-Waller factor is higher. Both facts perfectly reflect what is expected for metal nanoparticles. At the highest doping concentration (5%), the presence of Li favors the growth of a secondary NiO phase. Indeed, 2% Ni and 5% Li doped ZnO thin film shows %Ni sub = 75 � 11, %Ni met = 10 � 8, %NiO = 15 � 8. XANES studies further confirm that the substitutional Ni is more than 50% in all the samples. These results explain the observed magnetic properties. � 2013 IOP Publishing Ltd.

We report on anomalies in the dielectric and optical phonon spectra in bulk orthorhombic distorted perovskite LaCrO3 near an antiferromagnetic transition at 290 K. These anomalies were tracked using temperature dependent (200 K-320 K) dielectric and Raman spectroscopy. We observed a blue-shift for the B3g(3) optical phonon mode coincident with the onset of antiferromagnetic ordering of LaCrO3 in conjunction with a broad dielectric anomaly near the N�el temperature. The dielectric and optical phonon anomalies are discussed in the context of the observed antiferromagnetic transition in temperature dependent magnetic studies. � 2013 AIP Publishing LLC.

Titanium alloy (Ti6Al4V) substrates were deposited with smooth multilayer coatings, by hot filament chemical vapour deposition technique. The effect of boron doping on lattice parameter, residual stresses, hardness and coefficient of friction in multilayer-diamond coating system was studied. The frictional behaviour of the coatings was studied using a ball-on-disc micro-tribometer by sliding the coated samples of titanium alloy (Ti6Al4V) substrates against alumina (Al2O3) balls, and increasing normal load from 1 to 10 N. The average friction coefficient decreased from 0.36 to 0.29 for undoped multilayer-diamond coating system and from 0.33 to 0.18 for boron- doped (BD) multilayer-diamond coating system. The average indentation depths for undoped and BD multilayer- diamond coating systems were found to be equal to ∼>58 and ∼65 nm, respectively, and their hardness values were 60 and 55 GPa, respectively.

Piezoelectric response of AlN thin films was investigated in a AlN/Ti/Si(1 0 0) layer structure prepared by ion beam sputter deposition (IBSD) in reactive assistance of N+/ ions. The samples were characterized for their microstructure, piezoelectric response and charged defects using high resolution x-ray diffraction (HR-XRD), piezo force microscopy (PFM) and photoluminescence (PL) spectroscopy respectively. Our results show that the films are highly textured along the a-axis and charged native point defects are present in the microstructure. Phase images of these samples obtained from PFM show that the films are predominantly N-polar. The measured values of piezoelectric coefficient d 33(eff) for these samples are as high as 206 ± 20 pm V−1 and 668 ± 60 pm V−1 calculated by piezo response loop for AlN films of a thickness of 235 nm and 294 nm respectively. A mechanism for high d 33(eff) values is proposed with a suitable model based on the charged defects induced enhanced polarization in the dielectric continuum of AlN.

This work is focused on the development of a dual-layered diamond-coated tungsten carbide tool for machining titanium Ti-6Al-4V alloy. A hot-filament chemical vapor deposition technique was used to synthesize diamond films on tungsten carbide tools. A boron-doped diamond interlayer was added to a microcrystalline diamond layer in an attempt to improve the interface adhesion strength. The dual-layered diamond-coated tool was employed in machining at cutting speeds in the range of 70 to 150 m min−1 with a lower feed and a lower depth of cut of 0.5 mm rev−1 and 0.5 mm, respectively, to operate in the transition from adhesion- to diffusion-tool-wear and thereby arrive at suitable conditions for enhancing tool life. The proposed tool was then compared, on the basis of performance under real-time cutting conditions, with commercially available microcrystalline diamond, nanocrystalline diamond, titanium nitride and uncoated tungsten carbide tools. The life and surface finish of the proposed dual-layered tool and uncoated tungsten carbide were also investigated in interrupted cutting such as milling. The results of this study show a significant improvement in tool life and finish of Ti-6Al-4V parts machined with the dual-layered diamond-coated tool when compared with its uncoated counterpart. These results pave the way for the use of a low-cost tool, with respect to, polycrystalline diamond for enhancing both tool life and machining productivity in critical sectors fabricating parts out of titanium Ti-6Al-4V alloy. The application of this coating technology can also be extended to the machining of non-ferrous alloys owing to its better adhesion strength.

TmBa2Cu3O7- delta thin films have been grown in situ on LaAlO3 substrates using a pulsed laser ablation technique and the growth process studied at different growth temperatures. Highly c-axis oriented films with a high critical current density, Jc, of 2.5*106 A cm-2 at 77 K have been realized at optimum conditions at a relatively low substrate temperature of 700 degrees C. A systematic microstructural study and growth process is presented and discussed.

Er3+ doping at the La site in La0.8Sr0.2MnO3 showed an unusual increase in Curie/peak resistivity temperature (TC/TP) above a certain nominal dopant concentration (x⩾0.086). This increase is attributed to the presence of a cation-deficient ErMnO3 phase. Further, with increase in TP the overall resistivity of these compounds also decreases. We explain these results assuming the presence of a nanoscale mixture of charge-ordered antiferromagnetic insulating (CO-AFMI) phase in a ferromagnetic metallic matrix, wherein the increase in TC/TP with increase in Er3+ content is due to the local destruction of the CO-AFMI phase by the presence of the cation-deficient ErMnO3 phase. We thus provide an indirect evidence of electronic phase separation in these compounds.

We have investigated diffuse reflectance spectra of the polycrystalline BiFeO 3, Bi 0.9Ba 0.05Ca 0.05FeO 2.95, and Bi 0.9Ca 0.1FeO 2.95 samples to demonstrate crystal-field spectroscopy, which enabled us to explore local distortion in the non-centrosymmetric FeO 6 octahedron, and also to study chemical pressure effect on the band gap and d-d transition band energies. The energy values of band gap and d-d transition bands of the doped BiFeO 3 samples were found to red-shift with the reduced unit cell volume. Absorption spectroscopic studies of the BiFeO 3 samples reveal that nature of the band gap is a direct. Raman spectroscopy study also reveals that the softening/hardening of the certain Raman modes in BiFeO 3 upon substitution of Ca. The chemical pressure induced changes in the band gap and d-d band energies, and the Raman modes of the Ca doped BiFeO 3, which also found to enhance its magnetic and magnetoelectric properties. � 2012 American Institute of Physics.

Diamond thin films on non-carbide-forming metals such as copper have always had a large research potential because of the technological importance of copper as a substrate as well as its extensive use in microelectronic devices. However, the inability of copper to form carbides as well as the large mismatch in thermal expansion coefficients result in the generation of very high stresses in the coating that lead to delamination, film cracking, or other deleterious effects. We report on a method to increase the adherence of diamond coatings on copper substrates based on a surface modification process. A copper substrate is sandblasted in order to increase the surface roughness and surface area considerably. This process is expected to enhance the mechanical interlocking between the substrate and diamond film and has increased the seed density and surface energy as well. Microcrystalline diamond thin films were deposited on sandblasted copper substrates using hot filament chemical vapor deposition technique. Adhesion property of diamond coatings was evaluated by thermal quench technique combined with Raman spectroscopy. � 2012 by American Scientific Publishers.

Systematic substitutional studies in the Bi 2.1 Sr 1.93 Ca 0.97-x R x Cu 2 O 8+y (R=Pr,Gd,Er; 0≤x≤0.3 in steps of 0.05 and 0.4≤x≤0.97 in steps of 0.1) system were carried out in order to determine the effect of the magnetic moment and ionic radius of the rare-earth ion on the T c suppression rate. X-ray-diffraction studies indicate that the solid solubility of Gd and Er exists up to x=0.97 whereas that of Pr is limited to x=0.6 under the preparative conditions employed. Resistivity and ac susceptibility studies have shown that superconductivity persists up to x=0.4 and a metal-semiconductor transition occurs for x>0.4. The most interesting observation is that the rate of T c suppression for the superconducting phases is found to be identical for all rare earths. We have explained that hole filling rather than Abrikosov-Gor'kov pair breaking is responsible for the decrease in T c . The insulating phases with 0.5≤x≤0.97 exhibit the phenomenon of Mott's variable-range-hopping mechanism (VRH). The physical parameters related to VRH such as localization length (α −1 ), hopping range (R), and activation energy (W) for conduction, have been evaluated and discussed in detail.

Ho and Y doped ZnO nanoparticles were synthesized using a wet chemical route followed by structural, electrical and magnetic property characterization of the same. We present a comparison of the properties of Ho and Y (having same ionic radii) doped ZnO nanoparticles. X-ray diffraction studies of the diffraction data exhibit a monophasic wurtzite crystal structure similar to that of the parent compound, ZnO. Microstructural investigations of these samples by scanning electron microscopy show the presence of nanostructures. The optical measurements show an increase in the band gap of doped samples as compared to the undoped sample. DC magnetization measurements of Ho doped ZnO point towards the presence of hysteresis loop at 5 K with an Hc of about 110 Oe for a nominal 1 mol% Ho doped sample. The resistivity of Ho doped sample is found to be higher as compared to the undoped and Y doped sample. � 2011 Elsevier B.V. All Rights Reserved.

Cobalt ferrite nanoparticles were prepared by co-precipitation method and were heat treated at 100 oC, 200 oC, 400 oC and 600 oC for 2 h to increase the particle size. Phase purity of samples was confirmed by X-ray diffraction. Scherrer formula calculations showed crystallite size varied from 12 to 24 nm when heated from 100 oC to 600 oC. Transmission electron microscopy reveals a uniform and narrow particle size distribution about 12 nm for as-prepared cobalt ferrite particles. Room temperature saturation magnetization was found to vary from 40.8 to 67.0 emu/g as the particle size increased from12 nm to 24 nm. Increase in saturation magnetization with increase in particle size was attributed to the presence of magnetic inert layer on the surface of nanoparticles. Inert layer thickness calculated at 10 K and 300 K was 6 Å and 11 Å respectively. The dielectric properties ε’, tanδ, Z and θ have been studied as a function of frequency and particles size. For the 12 nm grain size, the dielectric constant is one order higher than that of bulk cobalt ferrite. Increase in the grain size showed an increase in the dielectric constant. The increase in the conductivity with grain size is mainly due to the grain size effects. The present study shows that the dielectric properties can be tailor-made to suit the requirement of a particular application by controlling the grain size.

Systematic studies of the Bi-2212 superconducting phase, substituting at the Cu-site by Fe and Co, have been carried out on an off-stoichiometric composition Bi 2.1 Sr 1.93 Ca 0.97 (Cu 2 − x M x )O 8 + y (M = Fe, Co; 0 ⩽ x ⩽ 0.12 for Fe and 0 ⩽ x ⩽ 0.1 for Co). For the x = 0 phase, T c,zero values in the range 74–76 K have been obtained consistently. X-ray diffraction studies show that the solid solubility exists up to x = 0.12 for M = Fe and x = 0.1 for M = Co. A monotonic decrease in T c with increasing dopant concentration is observed from resistivity as well as AC susceptibility measurements, and the results are discussed.

The effect of doping a magnetic ion like Co and a non-magnetic ion like Ga at the Mn-site in La0.7Ca0.3MnO3 was studied. ac magnetic susceptibility (χ) measurements show a large suppression in the ferromagnetic transition temperature (TC) for the Ga substituted compounds compared to that of the Co substituted compounds indicating that the decrease in ferromagnetic coupling in the former is due to smaller electronic bandwidth. The appearance of a prominent cusp in the χ–T curves for the Ga-compounds compared to the Co-compounds, even at low doping and also the deviation from the Curie–Weiss behaviour at low temperatures indicates a cluster glass kind of behaviour which is less pronounced in identical compositions of the Co-compounds. It has been seen that clustering of spins takes place either when the number of Mn4+ ions [J. Appl. Phys. 85 (1999) 1663] or when the number of mobile charge carriers is reduced [J. Magn. Magn. Mater. 214 (2000) L149]. In this case the number of Mn4+ ions is the same for identical compositions of Co and Ga-substituted compounds and hence the observed changes in TC can be attributed to the differences in the active electronic bandwidth. Resistivity measurements clearly confirm the presence of smaller electronic bandwidth in the Ga-compounds.

We have succeeded in growing a stable and ever eluding p-type (Li, Ni): ZnO using a codoping technique. Pulsed laser deposited (PLD) films grown in a small window of oxygen partial pressures (10−3–10−2 mbar) showed room temperature carrier density ∼ 2.1 × 10−17 cm−3. Ohmic properties of Ni/Au contact on p-ZnO films were studied using LTLM method. Efforts have also been made to grow different nano forms of ZnO and study their optical properties for various device application prospects.

We report the microstructural study of ZnO nanostructures: nanocombs, nanocones and microspheres, synthesized using a simple thermal evaporation technique. While nanocombs require the presence of a catalyst, nanocones and hollow ZnO microspheres have been synthesized on silicon substrate in absence of any catalyst or template material. ZnO hexagonal nanocones have been synthesized on Si(100) substrates by directly evaporating zinc acetate dihydrate, at a low temperature of 400 degrees C, without using any carrier gas. The possible mechanism of formation of these structures has been discussed in brief. Chemical composition analysis by energy dispersive X-ray spectroscopy shows an O rich condition of ZnO nanocones and oxygen deficient condition of nanocombs.

We report on the electronic energy-level diagram of polycrystalline ${\text{BiFeO}}_{3}$ using the elemental, optical, and current-density-electric field $(J\text{\ensuremath{-}}E)$ characteristics. The elemental, electronic composition, and valence-band structure of ${\text{BiFeO}}_{3}$ ceramics were studied using x-ray photoelectron spectroscopy. The diffuse reflectance spectrum of a mixture of ${\text{BiFeO}}_{3}$ and ${\text{BaSO}}_{4}$, used as a standard, was recorded to test the Kubelka-Munk model. From the graph of the Kubelka-Munk function versus wavelength, two charge-transfer bands and two doubly degenerated $d\text{\ensuremath{-}}d$ transitions (${^{6}\text{A}}_{1\text{g}}\ensuremath{\rightarrow}{^{4}\text{T}}_{2\text{g}}$ and ${^{6}\text{A}}_{1\text{g}}\ensuremath{\rightarrow}{^{4}\text{T}}_{1\text{g}}$) were observed in polycrystalline ${\text{BiFeO}}_{3}$. The $J\text{\ensuremath{-}}E$ curves measured on the ${\text{BiFeO}}_{3}$ ceramics showed space-charge-limited conduction mechanism.

In the present work we observe that the presence of catalysts give rise to morphologically different but similar nanostructures like nanobrushes and nanocombs respectively. A growth model suggesting the possible formation of these nanostructures has been proposed. Using a simple vapor deposition technique we have deposited ZnO thin films with a variety of fascinating nanostructures—nanobrushes and nanocombs. These unique nanostructures unambiguously demonstrate that ZnO probably has the richest family of nanostructures among all materials, both in structure and in properties. The as prepared sample exhibits visible green emission on UV excitation. Elemental mapping on the as prepared ZnO nanobrushes show presence of Zn and O.

In this paper, we report on the optical and electrical transport studies of TM ion (Ni, Ti, V, Fe, Cr, Mn, and Co) doped ZnO polycrystalline samples. Diffuse reflectance spectroscopy of doped ZnO showed the existence of absorption bands which were attributed to the d-d transitions of respective dopants. Electrical resistivity was found to decrease in case of Ti-, V-, Fe-, and Ni-doped ZnO bulk samples as compared to undoped. We explain the above behavior on the basis of impurity d -band splitting model. It is observed that with increase in dopant content the temperature range where variable-range hopping is valid shrinks to lower values and the activation energy lowers. Increase in characteristic temperature and decrease in localization length was observed with increase in TM ion content pointing towards the delocalization of electrons that sets in with doping. � 2009 The American Physical Society.

The ferrimagnetic spinel oxide Zn(x)Fe(3-x)O(4) combines high Curie temperature and spin polarization with tunable electrical and magnetic properties, making it a promising functional material for spintronic devices. We have grown epitaxial thin films with 0

We report on the structural, thermal, and magnetic properties of polycrystalline BiFeO3 synthesized by sol-gel route. Powder x-ray diffraction data of the BiFeO3 sample was refined with rhombohedral structure with space group R3c. Magnetization and coercive field measurements showed weak ferromagnetic nature below 10 K. We also investigated the low temperature magnetocaloric effect in polycrystalline BiFeO3 ceramics. The anomalies observed in the magnetic entropy change of the BiFeO3 ceramics were close to that of low temperature phase transitions. The combined relative errors in the magnetic entropy change are found to vary from 4% to 15% with increase in temperature. � 2009 American Institute of Physics.

The SrS:Ce/ZnS:Mn phosphor blends with various combination viz 75:25, 50:50 and 25:75 were assign to generate the white-light emission using near-UV and blue-light emitting diodes (LED) as an excitation source. The SrS:Ce exhibits strong absorption at 427 nm and the corresponding intense emission occurs at 480 and 540 nm due to electron transition from 5d(2D)-4f(2F5/2, 7/2) of Ce3+ ion as a result of spin-orbit coupling. The ZnS:Mn excited under same wavelength shows broad emission band with ?max=582 nm originates due to 3d (4G-6S) level of Mn2+. Photoluminescence studies of phosphor blend excited using near-UV to blue light confirms the emitted radiation varies from cool to warm white light in the range 430-600 nm, applicable to LED lightings. The CIE chromaticity coordinate values measured using SrS:Ce/ZnS:Mn phosphor blend-coated 430 nm LED pumped phosphors in the ratio 75:25, 50:50 and 25:75 are found to be (0.235, 0.125), (0.280, 0.190) and (0.285, 0.250), respectively. � 2009 Elsevier B.V. All rights reserved.

The anomalous Hall effect (AHE) has been studied systematically in the low-conductivity ferromagnetic oxide Fe$_{3-x}$Zn$_x$O$_4$ with $x = 0$, 0.1, and 0.5. We used (001), (110), and (111) oriented epitaxial Fe$_{3-x}$Zn$_x$O$_4$ films grown on MgO and sapphire substrates in different oxygen partial pressure to analyze the dependence of the AHE on crystallographic orientation, Zn content, strain state, and oxygen deficiency. Despite substantial differences in the magnetic properties and magnitudes of the anomalous Hall conductivity $\sigma_{xy}^{\rm AHE}$ and the longitudinal conductivity $\sigma_{xx}$ over several orders of magnitude, a universal scaling relation $\sigma_{xy}^{\rm AHE} \propto \sigma_{xx}^{\alpha}$ with $\alpha = 1.69 \pm 0.08$ was found for all investigated samples. Our results are in agreement with recent theoretical and experimental findings for ferromagnetic metals in the dirty limit, where transport is by metallic conduction. We find the same scaling relation for magnetite, where hopping transport prevails. The fact that this relation is independent of crystallographic orientation, Zn content, strain state, and oxygen deficiency suggests that it is universal and particularly does not depend on the nature of the transport mechanism., Comment: 4 pages, 4 figures

Monodispersed α–Fe2O3 nanoparticle aggregates with diameter ∼15 nm were successfully prepared by polyol process. The finite size effects in α–Fe2O3 nanoparticles were studied by X‐ray diffraction, transmission electron microscopy, diffuse reflectance spectroscopy and ac‐magnetic susceptibility. The optical band gap of α–Fe2O3 nanoparticles was significantly reduced compared to that of precursor. The α–Fe2O3 nanoparticles exhibited superparamagnetic behavior at room temperature, with blocking temperature TB = 100 K at 313 Hz and its value shifted to 124 K at 3.13 KHz. Analysis of ac‐magnetic susceptibility data gives a superparamagnetic relaxation time (τo) of 4×10−9 s.

Single phase Sr substituted BaZr0.1Ti0.9O3 (also known as BZT) ceramics with a formula Ba1-xSr xZr0.1Ti0.9O3 (x=0.10, 0.20, 0.30, 0.40 and 0.50) are prepared using a solid state reaction of mixed oxides at 1250 �C for 15 h. Analysis of XRD patterns of the ceramic powders show that Sr substitutes into Ba sites and reduces the lattice parameter. The powders are sintered at 1600 �C for 6 h to investigate the microstructure and functional properties. It is found that strontium substitution significantly modifies the microstructure and greatly influences the dielectric properties. The increase in Sr content reduces the ceramic grain size and results in spherical grains. With an increase in Sr content, the Curie temperature is lowered, and the relative permittivity maximum is increased and broadened. In Ba1-xSr xZr0.1Ti0.9O3 with x=0.30, the relative permittivity reached a maximum of 26600 and with further increase of Sr content, the relative permittivity is lowered and the phase transition is found to be broad and diffused. The ferroelectric hysteresis characteristics are discussed in detail. � 2007 Springer-Verlag.

ZnO is a unique material that offers about a dozen different application possibilities. In spite of the fact that the ZnO lattice is amenable to metal ion doping (3d and 4f), the physics of doping in ZnO is not completely understood. This paper presents a review of previous research works on ZnO and also highlights results of our research activities on ZnO. The review pertains to the work on Al and Mg doping for conductivity and band gap tuning in ZnO followed by a report on transition metal (TM) ion doped ZnO. This review also highlights the work on the transport and optical studies of TM ion doped ZnO, nanostructured growth (ZnO polycrystalline and thin films) by different methods and the formation of unique nano- and microstructures obtained by pulsed laser deposition and chemical methods. This is followed by results on ZnO encapsulated Fe3O4 nanoparticles that show promising trends suitable for various applications. We have also reviewed the non-linear characteristic studies of ZnO based heterostructures followed by an analysis on the work carried out on ZnO based phosphors, which include mainly the nanocrystalline ZnO encapsulated SiO2 ,an ew class of phosphor that is suitable for white light emission. (Some figures in this article are in colour only in the electronic version)

The structural and photoluminescent (PL) properties of Zn2(1-x)MnxSiO4 (1 ? x? 5) thin film phosphors grown using a pulsed laser deposition technique have been investigated. The effect of systematic variation of oxygen partial pressures (O2 pp) (100, 300, 500 and 700 mTorr) during the growth of these thin films has been studied. Thin film grown on silicon substrate at 750 �C and in situ annealed in 300 mTorr of O2 pp exhibits superior PL property; ex situ annealing at higher temperatures improves the PL intensity. � 2007 Acta Materialia Inc.

Single-phase nanocrystalline powder of barium zirconium titanate, Ba(ZrxTi1-x)O3 (BZT), x = 0.10, 0.20 and 0.30, was synthesized at low-temperature using an aqueous co-precipitation technique. X-ray diffraction (XRD) of the as-precipitated powder showed single-phase BZT formation. The decrease in precipitant concentration resulted in impurity barium carbonate phase formation. Transmission electron microscopy studies of as-prepared powders showed an average particle size of 30 nm and the crystallite size from XRD was estimated to be 13 nm. The microstructural studies of sintered bodies showed an average grain size of 4 ?m and the dielectric and ferroelectric behaviour of BZT with 10 mol.% Zr is reported. � 2007 Acta Materialia Inc.

Reference EPFL-ARTICLE-216393doi:10.1088/0022-3727/48/50/500302View record in Web of Science Record created on 2016-02-16, modified on 2017-05-12

We demonstrate that oxygen vacancies (VO) produced by aliovalent (Ca2+) doping in BiFeO3 (BCFO) and associated structural changes due to VO ordering result in systematic alteration of the bandgap (Eg) over a wide range from 1.5 eV to 2.3 eV. By contrast, the change in the bandgap of a Ca2+ and Ti4+ co-doped BiFeO3 (BCFTO) system, wherein the VO formation is suppressed, is negligible. These contrastive results strongly confirm the role of oxygen vacancies in altering the bandgap of BCFO. Irrespective of doping, microstrain, which is found to be large (0.3 to 1.2%) below a critical size (dc ~ 60 nm) also produces a small, yet linear change in the bandgap (Eg from 2.0 to 2.3 eV). The cubic phase stabilizes gradually in BCFO for x > 0.1 through an orthorhombic phase (for 0.05 0.1 in BCFTO. This change in BCFO at 300 K suggests a high-pressure-like (or high-temperature-like) effect of the oxygen vacancies and dopants on the structure. Systematic variations in the relative intensities and peak positions of Fe d–d transitions in BCFO reveal the local changes in Fe–O–Fe coordination. These results along with XANES and HRTEM studies substantiate the observed structural changes.

We have systematically investigated hydrogen sensing properties of pulsed laser deposited palladium thin films with reference to their crystallinity, surface morphology and film thickness. Thin films were deposited on clean quartz substrates at varying growth parameters. Structural and surface morphological characterizations have been carried out using X-ray diffraction, scanning electron microscopy and atomic force microscopy. Thin films with nanostructured surface morphology were achieved. Electrical resistance measurements, carried out in situ, by a two-probe technique in a chamber with a provision to introduce a known concentration of hydrogen gas and air, showed saturation on exposure to hydrogen gas. The change in electrical resistance due to hydrogen loading is found to be reversible. The sensor response time is typically 10-20 s. The Pd films are stable after several cycles of hydrogenation and dehydrogenation. � 2006 IOP Publishing Ltd.

Structural and photoluminescence (PL) properties of Zn2(1-x)MnxSiO4 (1 ≤ x ≤ 5) and diffuse reflectance spectroscopy (DRS) and morphological studies of ZnGa2O4:Mn thin film green emitting phosphors grown using pulsed laser deposition (PLD) technique have been investigated. Zn2(1-x)MnxSiO4 thin films grown on Si substrate at 700°C in 300 mTorr of oxygen partial pressure, upon ex-situ annealing at higher temperatures exhibit superior PL intensity. ZnGa2O4:Mn phosphor thin films grown on quartz substrate at 650oC and in-situ annealed in 300mTorr of oxygen partial pressure show better emission intensity. For both Zn2SiO4:Mn and ZnGa2O4:Mn phosphors, luminescence can be assigned to 4T1 – 6A1 transition of Mn2+ within the 3d orbital giving rise to emission at 525 and 503 nm, respectively.

In this work the ferromagnetic state in a ferromagnetic insulating manganite viz. Pr0.8 Sr0.2 Mn O3 was analyzed. The temperature variation of ac susceptibility is seen to show two transitions with a high temperature transition occurring at 158 K and a low temperature cusp (Tf) around 90 K. The high temperature transition (TC) was found to be independent of frequency while the low temperature transition shifts with frequency indicating a frustrated magnetic state. The relaxation time observed from the critical slowing down spin analysis indicates that this state is that of a cluster glass. Temperature variation of resistivity shows an insulating behavior with two distinct humps corresponding to TC and Tf. Temperature variation of thermopower exhibits a peak at TC and decreases below TC which is attributed to the sudden release of holes from traps, similar to a ferromagnetic metallic manganite. Magnetoresistance is seen to show a change in curvature upon cooling the sample across TC which in conjunction with the peak in resistivity and thermopower suggests that this transition is mediated by a double exchange mechanism. The frustrated state is seen to arise because of a competition between double exchange and superexchange mechanisms. The effect of double exchange mechanism is seen to persist all the way down to 5 K as seen from the magnetoresistance analysis. These results clearly suggest that double exchange still plays an important role in dictating the magnetic and electrical properties in ferromagnetic insulating manganites. � 2006 American Institute of Physics.

The effect of doping of transition metal ions (Fe and Co) on transport properties of ZnO has been studied in both bulk and thin films. The solubility limit of these ions have been found to be higher in thin films compared to bulk. Optical measurements reveal the presence of Fe in both 2+ and 3+ state. Co is believed to be in 2+ states. Electrical resistivity measurements show that while for bulk Fe doped ZnO samples there is a decrease in resistivity compared to undoped ZnO, it increases for bulk Co doped ZnO samples. However, thin film samples of both types of doped compounds show a decrease in resistivity compared to undoped ZnO. This difference in bulk and thin film behaviour has been explained on the basis of experimental results.