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Lead-free piezoelectric ceramics of (1 − x)K0.5Na0.5NbO3-xCaTiO3 were fabricated, and their crystal structure, microstructure, and electrical properties were systematically studied. Rietveld refinement of the x-ray diffraction data and Raman spectroscopic analyses revealed a composition-dependent structural phase transition: three phase transitions, namely, from a pure orthorhombic phase for x ≤ 0.02 to a mixed phase of orthorhombic and tetragonal phases (0.03 ≤ x ≤ 0.08) and finally another mixed phase of tetragonal + cubic for x = 0.10 and 0.15 at room temperature (RT). The morphological study reveals a decrease in grain size along with a more uniform distribution of grains as the concentration of CaTiO3 (CT) increases; notably, a homogeneous distribution of grains is observed for x = 0.05. The temperature-dependent dielectric properties show two phase transitions, from orthorhombic to tetragonal (TO-T) and tetragonal to cubic (TC), for unmodified K0.5Na0.5NbO3 (KNN). However, both the phase transition temperatures (TO-T and TC) decrease, and the transition peaks broaden with an increase in CT substitution, and for x > 0.06, the TO-T shifted below RT. The broadening of the transition peak at TO-T may be due to the relaxation behavior. Among the prepared samples, the 5 mol. % CT-modified KNN shows the optimum electrical properties (d33 = 114 pC/N, ɛr = 412, and 2Pr = 15.25 μC/cm2) at RT. The enhanced electrical properties for x = 0.05 are due to the coexistence of orthorhombic and tetragonal phases, facilitating easy polarization rotation and flattening of the free energy profile. A phase diagram has been constructed based on the information gathered from the temperature-dependent dielectric measurements, RT x-ray diffraction, and Raman spectroscopy data and is discussed in detail. [ABSTRACT FROM AUTHOR]

Multiferroic composites consisting of a single-phase multiferroic [0.6(PbZr0.53Ti0.47O3)-0.4(PbFe0.5Ta0.5)O3] as a matrix and a magnetostrictive phase (Co0.6Zn0.4Fe1.7Mn0.3O4) dispersed in the matrix are fabricated via hybrid synthesis technique. The structure and surface morphology studies using x-ray diffraction and field emission scanning electron microscopy techniques indicate the formation of 3-0 type particulate composites. Coexistence of soft-magnetic behavior and ferroelectric characteristics are confirmed for composites from magnetization vs magnetic field (M–H) and polarization vs electric field (P–E) measurements, respectively. Magneto-dielectric (MD) measurement shows significant changes in the dielectric properties with the application of a magnetic field, indicating the existence of strong MD behavior. The biquadratic nature of magneto-electric (ME) coupling is described by the Landau free energy equation arising from the strain transfer at the interfaces between the constituent phases. The direct magneto-electric voltage coefficient measurement also confirms very strong coupling between ferroelectricity and magnetism and supports the strain-mediated magneto-electric effect in composites. The Φ = 0.3 composite exhibits the maximum ME coefficient of 20.72 mV/cm Oe with MS = 24.62 emu/g, HC = 59.66 Oe, and piezoelectric coefficient value d33 = 19 pC/N. The strong magneto-electric effect along with low dielectric loss at room temperature in these composites suggests their suitability for multifunctional magneto-electric device applications such as magnetic sensors, etc. [ABSTRACT FROM AUTHOR]

Here, we have studied the phase transition and magneto-electric properties of a 70 wt. % Pb(Fe0.5Nb0.5)O3–30 wt. % Co0.6Zn0.4Fe1.7Mn0.3O4 (70 wt. % PFN–30 wt. % CZFMO) multiferroic composite that exhibits a maximum magneto-electric (ME) coefficient of 26.78 mV/cm Oe at room temperature. Raman analysis confirms the formation of composite and development of strain with the shifting of Raman modes. The local symmetry breaking of end members of the composite is observed by the splitting of Raman modes. The first-order derivative of magnetization with temperature (dM/dT vs T) shows anomalies across 140 K due to the PFN phase, whereas the anomaly around 250 K is due to the spin glass transition of the CZFMO phase. The magnetization vs magnetic field (M–H) study at different temperatures reveals the existence of superparamagnetic behavior above 300 K. The temperature-dependent dielectric behavior of the composite shows an anomaly around ferroelectric phase transition (Tm) for the PFN phase along with the broad relaxation peak arising due to the CZFMO phase. The linear behavior of magnetocapacitance (MD%) with the square of magnetization (M2) suggests the existence of biquadratic ME coupling. The ME study on the composite suggests the existence of both direct and converse ME effects. [ABSTRACT FROM AUTHOR]

Magnetoelectric (ME) composite thin films are promising candidates for novel applications in future nanoelectronics, spintronics, memory, and other multifunctional devices as they exhibit much higher ME coupling and transition temperatures (Tc) than well-known single phase multiferroics discovered to date. Among the three types of multiferroic composite nanostructures, (2–2) layered and (1–3) vertically aligned composite nanostructures exhibit comparatively smaller ME coupling due to different shortcomings that restrict their use in many applications. Here, we study the morphological, piezoresponse force microscopic (PFM), ferroelectric, magnetic, and magnetodielectric properties of 0–3 [magnetic nanoparticles (0) homogeneously distributed in ferroelectric matrices (3)] multiferroic composite thin films. The Pb(Fe0.5Nb0.5)O3 (PFN)–Ni0.65Zn0.35Fe2O4 (NZFO) particulate composite films were synthesized by pulsed laser deposition. These particulate composite thin films are completely c-axis oriented with very low surface roughness. We observed magnetic and ferroelectric Tc above room temperature (RT) for all composite thin films. The PFN–NZFO 0–3 composites exhibit large polarization, high saturated magnetization with low coercive field, and low dielectric loss along with magnetodielectric coupling at RT. These nanocomposites might be utilized in next generation nano/microelectronics and spintronic devices. [ABSTRACT FROM AUTHOR]

Recent advancements in computing technologies coupled with the need to make sense of large amounts of raw data have renewed much interest in data-driven materials design and discovery. Traditional materials science research relies heavily on experimental data to gauge the properties of materials. However, this paradigm is purely based on trial and error and ongoing research can take decades to discover new materials. Data-driven modeling tools such as machine learning and its proven libraries can help speed up the materials' discovery process through the implementation of powerful algorithms on readily available material datasets mined from the ever-increasing private- and government-funded material databases. In this Perspective, we applied various machine learning models on tens of hundreds of thermoelectric compounds obtained from density functional theory calculation results. In our preliminary analysis, we made use of pymatgen and the powerful materials science library matminer to add and explore key material features that have the propensity to accurately predict our achievable target output. We evaluated the accuracy and performance of our models with the coefficient of determination (R2), the root mean square error, and K-fold cross-validation metrics and identified the most important descriptors for our materials. Finally, we reviewed the current state-of-the-art in data-driven thermoelectric materials' design and discovery, its current challenges, and prospects. [ABSTRACT FROM AUTHOR]

Vanadium oxide (VO2) thin films have drawn significant research and development interest in recent years because of their intriguing physical origin and wide range of functionalities useful for many potential applications, including infrared imaging, smart windows, and energy and information technologies. However, the growth of highly epitaxial films of VO2, with a sharp and distinct controllable transition, has remained a challenge. Here, we report the structural and electronic properties of high quality and reproducible epitaxial thin films of VO2, grown on c-axis oriented sapphire substrates using pulsed laser deposition at different deposition pressures and temperatures, followed by various annealing schedules. Our results demonstrate that the annealing of epitaxial VO2 films significantly enhances the Semiconductor to Metal Transition (SMT) to that of bulk VO2 transition. The effect of oxygen partial pressure during the growth of VO2 films creates a significant modulation of the SMT from around room temperature to as high as the theoretical value of 68 °C. We obtained a bulk order transition ≥104 while reducing the transition temperature close to 60 °C, which is comparatively less than the theoretical value of 68 °C, demonstrating a clear and drastic improvement in the SMT switching characteristics. The results reported here will open the door to fundamental studies of VO2, along with tuning of the transition temperatures for potential applications for multifunctional devices. [ABSTRACT FROM AUTHOR]

With the rapid development of new device miniaturization technology, there is invigorated interest in magnetic nanostructures for potential application in novel multifunctional devices. In continuation to our search for a suitable magnetic material having Curie temperature (Tc) well above room temperature for multifunctional applications, we have studied the dielectric, optical, magnetic, and resistance switching characteristics of Ni0.65Zn0.35Fe2O4 (NZFO) thin films. The observation of only (004) reflection in the X-ray diffraction patterns confirms the c-axis orientation and high quality growth of NZFO thin films. The presence of mixed valences of Fe2+/Fe3+ cations is probed by X-ray photon spectroscopy, which supports the cationic ordering-mediated large dielectric response. Our investigations reveal NZFO to be an indirect band gap material (~1.8eV) with a direct gap at ~2.55eV. These nanostructures exhibit high saturation magnetization and a low coercive field with a ferrimagnetic-paramagnetic phase transition of ~713K. Magnetic force microscopy studies revealed the stripe-like domain structure of the investigated thin films. In addition, these thin films exhibit reliable and repeatable unipolar resistive switching characteristics. The observed high dielectric permittivity with low loss tangent, large magnetization with soft magnetic behavior, striped magnetic domain structure and reliable resistance switching in NZFO thin films above room temperature suggest potential application in memory, spintronics, and multifunctional devices. [ABSTRACT FROM AUTHOR]

The effects of disorder on the magnetic phases as well as on the conduction process are extensively studied in LaFeO3 nanoparticles in a wide field and temperature ranges. The disorder induced by Na in LaFeO3 alters its robust magnetic phase to the coexistence of distinctly different magnetic orders. The phase purity of the samples, which plays an important role, is detected by synchrotron x-ray diffraction. Detailed magnetic measurements are carried out to investigate the evolution of phases due to substitutions. The samples show the coexistence of a superparamagnetic phase along with a weak ferromagnetic phase, and the ratio of the two distinct phases varies with substitutions. The Mössbauer measurement supported the said magnetic phases in the samples. The X-ray photoelectron spectroscopy analysis clarifies the simultaneous presence of Fe3+ and Fe4+ due to Na+ incorporation. Furthermore, the electrical conduction is found to be greatly influenced by such substitutional disorder. From the dielectric measurement, a p-type polaronic conduction mechanism is found in 25% Na incorporation, which is mainly due to the hole hopping between Fe4+ and Fe3+ states. The semicircles in the whole temperature range in the Cole–Cole plots of impedance and modulus spectra are the co-contribution of the grain and the grain boundary effect in the conduction process. [ABSTRACT FROM AUTHOR]

Pure hydroxyapatite (HAp) semiconducting microrods with very low dielectric loss have been synthesized in aqueous media of pH values 6, 8, and 10 by the hydrothermal method. Samples are characterized by X-ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Fourier transform infrared spectra analyses. The optical bandgap energies of these samples are found to be within the semiconducting range (∼3–4 eV). FESEM and TEM image analyses reveal the formation of microrods and reduction of the average length of the rods with increasing pH values. A core-shell-like microrod structure has been observed in the sample with pH value 6. The charge carrier follows an adiabatic small polaron hopping mechanism. The dielectric loss values are very small compared to that of other ceramic oxides which is very advantageous for electronic applications. Correlated barrier hopping model is the dominant charge transport mechanism within the samples with maximum barrier heights of 0.25 eV, 0.26 eV, and 0.27 eV for samples with pH values 6, 8, and 10, respectively. Nonideal Debye type relaxation appears within the material when the AC field is applied for temperatures above 100 °C. [ABSTRACT FROM AUTHOR]

Magnetoelectric (ME) materials with ferroelectric and magnetic transition temperatures near room temperature are of current interest in research due to their technological importance and potential applications. Herein, we report the coupled magnetic ordering and phonons in gallium ferrite (GaFeO3), a near room temperature ME perovskite, using magnetization and inelastic light scattering measurements as a function of temperature. Temperature-dependent magnetization behavior studied in a wide temperature range of 5–395 K at both field-cooled (FC) and zero-field-cooled (ZFC) conditions using different static magnetic fields confirms the magnetic transition temperature Tc at 220 K. On temperature dependent Raman spectroscopy, no significant changes in Raman spectra were observed at an elevated temperature that can be attributed to the absence of structural phase transition. Instead of expected anharmonic behavior, several librational (rigid rotation) and stretching modes of rigid BO6 units were found to be hardening below Tc, suggesting the significant magnetoelastic coupling contributions to phonon frequencies. The asymmetric stretching mode at 753 cm−1 is found to have larger spin-phonon coupling contribution (λ∼2.93), while the lattice mode at 153 cm−1 and external librational mode at 240 cm−1 had the lowest effect (λ∼0.88). [ABSTRACT FROM AUTHOR]

We report the intense room temperature ultraviolet photoluminescence (PL) emission from self-assembled vertically aligned ZnO nanorods grown directly on graphene. The PL intensities from ZnO nanorods grown on other van der Waal bulk solids such as highly oriented pyrolytic graphite and mica under the same experimental condition are also compared. The enhanced PL signal from ZnO nanorods grown on graphene is explained on the basis of lattice matching of ZnO with that of graphene leading to high crystal quality. Furthermore, the role of graphene plasmons on the enhanced PL signal is explored by studying the micro-PL mapping on a single nanorod lying horizontally on the graphene surface. The uniform and high PL intensity distribution is noticed along the central axis of the rod, and the intensity distribution decreases toward either side of the central axis. The occurrence of such intensity distribution is explained by resonant excitation of graphene plasmon near bandgap energy of ZnO, which is modulated by surface corrugation of graphene and followed by its transformation into the propagating photon. [ABSTRACT FROM AUTHOR]

Substrate-induced electron energy band alignments of ultrathin molybdenum disulfide (MoS2) films are investigated using photoemission spectroscopy. Thin layer MoS2/Al2O3 and MoS2/ZrO2 interfaces show valence band offset (VBO) values of 3.21 eV and 2.77 eV, respectively. The corresponding conduction-band offset (CBO) values are 3.63 eV and 1.27 eV. Similarly, the calculated VBO and CBO values for an ultrathin layer of MoS2/SiO2 are estimated to be 4.25 and 2.91 eV, respectively. However, a very thick layer of MoS2 on Al2O3 and ZrO2 layers increases the CBO and VBO values by 0.31 eV and 0.2 eV, respectively, due to the shifting of the Mo 4dz2 band toward the Fermi level. The atomic force microscopy images show that the films are atomically smooth and favor the formation of a high-quality interface between the substrate and the film. The investigated luminescence spectra reveal that the MoS2 films show very strong interactions with different high-k surfaces, whereas the Raman spectrum is only weakly influenced by the different dielectric substrates. This interesting finding encourages the application of high-k oxide insulators as gate materials in MoS2-based complementary metal-oxide semiconductors and other electronic devices. [ABSTRACT FROM AUTHOR]

Layered structure bismuth telluride and molybdenum disulfide thin films were successfully deposited on different substrates using radio-frequency magnetron sputtering technique. The structural, morphological, and thermoelectric transport properties of bismuth telluride and molybdenum disulfide thin films have been investigated systematically to fabricate high-efficient thermal energy harvesting thermoelectric device. The magnitude of the Seebeck coefficient of bismuth telluride thin films decreases with increase in film thickness. Bismuth telluride grown at 350 °C for 10 min, which is approximately 120 nm, displays a maximum Seebeck coefficient of −126 μV K−1 at 435 K. The performance shows strong temperature dependence when the films were deposited at 300 °C, 350 °C, and 400 °C. The power factor increases from 0.91 × 10−3 W/mK2 at 300 K to about 1.4 × 10−3 W/mK2 at 350 K. Molybdenum disulfide films show the positive Seebeck coefficient values and their Seebeck coefficient increases with film thickness. The AFM images of bismuth telluride thin films display a root-mean-square (rms) roughness of 32.3 nm and molybdenum disulfide thin films show an rms roughness of 6.99 nm when both films were deposited at 350 °C. The open-circuit voltage of the pn-junction thermoelectric generator (TEG) device increases with increase in ΔT to about 130 mV at ΔT = 120 °C. We have demonstrated a highly efficient pn-junction TEG device for waste heat recovery applications. [ABSTRACT FROM AUTHOR]

We report systematic studies on crystal structure and magneto-dielectric properties of (1-x) BiFeO3-x DyMnO3 (0.0⩽x⩽0.2) nanoceramics synthesized by auto-combustion method. Rietveld refinement of X-ray diffraction data indicates a structural transition from R3c to R3c + Pn21a at x=0.1. Field emission scanning electron micrographs display a decrease in grain size with increase in x. The presence of dielectric anomalies around antiferromagnetic transition temperature implies the magnetoelectric coupling. Dielectric measurements showed decrease in magnetic ordering temperature with increasing x in agreement with differential scanning calorimetry results. A significant increase in magnetization has been found with increasing DyMnO3 substitution. Magnetoimpedance spectroscopy reveals a significant change (∼18%) in dielectric permittivity at H=2T for x=0.2. [ABSTRACT FROM AUTHOR]

We report the crystal structure, dielectric, transport, and magnetic properties of Ni0.65Zn0.35Fe2O4. Rietveld refinement results of X-ray diffraction patterns confirm the phase formation of the material with cubic crystal structure (Fd3m). The frequency dependent ac conductivity behavior obeys the Jonscher's power law and is explained using the jump relaxation model. The observed behavior of temperature dependent bulk conductivity is attributed to the variable-range hopping of localized polarons. The correlation of polaron conduction and high permittivity behavior of NZFO is established on the basis of long range and short range conduction mechanisms. The complex impedance spectra clearly show the contribution of both grain and grain boundary effect on the electrical properties. [ABSTRACT FROM AUTHOR]

We report the crystal structure, dielectric, transport, and magnetic properties of Ni0.65Zn0.35Fe2O4. Rietveld refinement results of X-ray diffraction patterns confirm the phase formation of the material with cubic crystal structure (Fd3m). The frequency dependent ac conductivity behavior obeys the Jonscher's power law and is explained using the jump relaxation model. The observed behavior of temperature dependent bulk conductivity is attributed to the variable-range hopping of localized polarons. The correlation of polaron conduction and high permittivity behavior of NZFO is established on the basis of long range and short range conduction mechanisms. The complex impedance spectra clearly show the contribution of both grain and grain boundary effect on the electrical properties. [ABSTRACT FROM AUTHOR]

We report the crystal structure, magnetic, ferroelectric, dielectric, and magneto-dielectric properties of [Pb(Fe0.5Nb0.5)O3](1-x)[Co0.65Zn0.35Fe2O4]x: (x = 0.1, 0.2, 0.3, and 0.4) composites. Rietveld refinement results of X-ray diffraction patterns confirm the formation of these composites for all x values. All the composites show well-saturated ferroelectric and ferromagnetic hysteresis (multiferroic-composite behavior) at room temperature. With increase in Co0.65Zn0.35Fe2O4 (CZFO) content an increase in saturation magnetization, and decrease in saturation polarization, remanent polarization, and dielectric constant are observed. The ferroelectric phase transition temperature increases with increase in CZFO content. All of the compositions undergo second-order ferroelectric phase transitions, which can be explained by Landau-Devonshire theory. The recoverable energy density (∼0.20 to 0.04 J/cm3) and charge-curve energy density (∼0.84 to 0.11 J/cm3) decrease with increase in the CZFO content. The room-temperature magneto-dielectric measurements provide direct evidence of magneto-electric coupling via strain at room temperature. [ABSTRACT FROM AUTHOR]

Thin films of vanadium dioxide (VO2) are deposited on indium tin oxide (ITO), stainless steel (SS), and glass substrates using chemical vapour deposition. X-ray diffraction and Raman spectroscopy measurements confirmed the single phase nature of the VO2, which showed a phase transition from a low conducting state at low temperature(<68 °C) to a high conducting state at high temperature (>68 °C). This was confirmed by electrical conductance and infra-red reflectance measurements. X-ray photoelectron spectroscopy was used to measure the charge states of vanadium species. The optical constants of VO2 were determined using visible and near-infra red(NIR) reflectivity and show that the VO2 film on ITO has a lowered plasma frequency compared with VO2 on glass substrates. The thin films of VO2 enable a broadband of ultra-high absorption at mid-wave infra-red frequencies due to a Fabry-Pérot (F-P) like resonance due to the dielectric properties of ITO, SS, or glass. The tunability of this absorption band via VO2 thickness and the switchability by temperature makes the system attractive for absorptive coatings with controllable emissivity. [ABSTRACT FROM AUTHOR]

The search for a room temperature single phase multiferroic material displaying strong magnetoelectric coupling and low leakage current for practical device applications has been underway and a long-standing challenge. In continuation to our investigations for achieving robust ME coupling and enhanced electrical insulation at room temperature, we report magnetic, electrical insulation, and magneto-dielectric properties of Nd and Mn co-doped BiFeO3 (Bi0.95Nd0.05)(Fe0.97Mn0.03)O3 (BNFM) polycrystalline electro-ceramics. Magnetic studies have been carried out in two different temperature regions, i.e., 15–300K and 300–800K. The doping of Nd and Mn in the BiFeO3 (BFO) lattice slightly reduces the Néel temperature (TN) with broad weak ferromagnetic (FM) to paramagnetic (PM) phase transition by increasing ferromagnetic domain fractions. A small amount of magnetic frustration is also found in the low temperature regions, below 300K at fields of 100 and 200Oe, and below 200K at higher field cooled and zero field cooled; this may be due weak long range ordering and small magnitude of magnetic moments. High temperature magnetic results imply the existence of a weak ferromagnetic phase with a FM to PM phase transition around 630K (±5K) and significant suppression of the spin frustration and canting properties of BFO. The Nd and Mn co-doping also substantially improved the electrical insulating properties of BFO. The leakage current analysis suggests that the Simmons’ mechanism is probably a dominant conduction mechanism in BNFM at room temperature. The observation of dielectric anomaly around the TN and significant variation of dielectric parameters with different static magnetic field in BNFM implies the existence of strong magnetodielectric coupling. The enhanced magnetic and electrical insulation properties with strong magnetodielectric coupling at room temperature elucidate the possible potential candidates for multifunctional and spintronics device applications. [ABSTRACT FROM AUTHOR]

We report on high performance transparent Al:ZnO (AZO) thin film heaters on flexible polymer (polyethylene terephthalate) and glass substrates which demonstrate low sheet resistivity. AZO thin films were grown by radio-frequency magnetron sputtering at low Ts (below 200°C) on flexible, transparent polyethylene terephthalate substrates that show stable and reproducible results by applying low (<10 V) voltages. This study also examined identical AZO thin films on glass substrates that showed highly reproducible heating effects due to the Joule heating effect. The potential applications are foldable and wearable electronics, pain/injury therapy smart windows, automobile window defrosters, and low-cost power electronics. [ABSTRACT FROM AUTHOR]

We report the crystal structure, dielectric, magnetic, and magneto-electric properties of (1-x) BiFeO3-xYMnO3 (0.00 ≤ x ≤ 0.2) multiferroic nanoceramics prepared by auto-combustion technique. YMnO3 substitution is found to induce a structural phase transition from R3c to R3c+Pbnm after x ≈ 0.1 using Rietveld refinement technique. Field emission scanning electron micrographs show decrease in grain size with increase in YMnO3 content. The dielectric permittivity and loss tangent are found to be increased with composition x. The anomalies noticed from the temperature dependent dielectric analysis reveal the signature of magneto-electric coupling in the system. A decrease in magnetic ordering temperature as a function of composition is found from dielectric study. At room temperature, the dielectric permittivity of all the YMnO3 modified samples decrease with increasing magnetic field. The maximum value of magneto-electric coupling coefficient ([variant_greek_epsilon](H)-[variant_greek_epsilon](0))/[variant_greek_epsilon](0) is found to be ∼ -5.5% at H = 2 T for x = 0.2. The behaviour of the magnetic hysteresis loop observed at room temperature suggests the suppression of space modulated spin structure. [ABSTRACT FROM AUTHOR]

We investigate the structural and electronic properties of VO2 thin films on c-plane sapphire substrates with three different surface morphologies to control the strain at the substrate-film interface. Only non-annealed substrates with no discernible surface features (terraces) provided a suitable template for VO2 film growth with a semiconductor-metal transition (SMT), which was much lower than the bulk transition temperature. In addition to strain, oxygen vacancy concentration also affects the properties of VO2, which can be controlled through deposition conditions. Oxygen plasma-assisted pulsed laser deposition allows favorable conditions for VO2 film growth with SMTs that can be easily tailored for device applications. [ABSTRACT FROM AUTHOR]

We report the growth of high indium content InGaN:Yb nanorods grown on c-plane sapphire (0001) substrates using plasma assisted molecular beam epitaxy. The in situ reflection high energy electron diffraction patterns recorded during and after the growth revealed crystalline nature of the nanorods. The nanorods were examined using electron microscopy and atomic force microscopy. The photoluminescence studies of the nanorods showed the visible emissions. The In composition was calculated from x-ray diffraction, x-ray photoelectron spectroscopy, and the photoluminescence spectroscopy. The In-concentration was obtained from photoluminescence using modified Vegard's law and found to be around 37% for InGaN and 38% for Yb (5±1%)-doped InGaN with a bowing parameter b=1.01 eV. The Yb-doped InGaN showed significant enhancement in photoluminescence properties compared to the undoped InGaN. The Yb-doped InGaN nanorods demonstrated the shifting of the photoluminescence band at room temperature, reducing luminescence amplitude temperature dependent fluctuation, and significant narrowing of excitonic emission band as compared to the undoped InGaN. The magnetic properties measured by superconducting quantum interference devices reveals room temperature ferromagnetism, which can be explained by the double exchange mechanism and magnetostriction. [ABSTRACT FROM AUTHOR]

We report on the effects of stacking of the macrocycles in atomic layer deposited (ALD) Al:ZnO thin films on the structural and electrical properties. There is a large change in the resistivity ranging from as high as 1.19×10-3 Ω cm for 760 growth cycles film down to as low as 7.9×10-4 Ω cm for the 4000 cycles. The electrical transport demonstrates a transition from a semiconductor behavior at 760 cycles to a metallic behavior in the 4000 cycle, due to an increase in electron scattering as well as increase in the carrier concentration. However, interestingly the carrier concentration sharply increases with increasing macrocycles containing Al and Zn, exhibiting a nearly metal-like behavior in thicker films. We anticipate that the change in Zn-vacancy, Vzn, formation energy is related to the increase in surface area of the ALD precursor deposition plane. The increase in Vzn density allows for more adsorption of Al-precursor into the doped monolayer, showing interesting electrical properties. [ABSTRACT FROM AUTHOR]

We report magnetoelectric coupling and Raman spectroscopic studies on [(1 - x)Pb(Fe0.5Nb0.5) O3-xNi0.65Zn0.35Fe2O4] (x=0.20) PFN-NZFO composite. Apart from the presence of zone centre Raman active modes of the parent compound, some new peaks are observed in the low frequency region. The electric field controlled peak position (∼48 cm-1) suggests that this mode is of magnetic origin. From temperature dependent Raman scattering studies, temperature coefficients for phonons of different symmetries were estimated. Our measurements on electrical control of magnetic order and magnetic control of electrical order confirmed the existence of converse and direct magnetoelectric coupling in this composite at room temperature. [ABSTRACT FROM AUTHOR]

We report on the study of epitaxial MgO thin films on (0001) Al-doped ZnO (Al: ZnO) underlayers, grown by oxygen plasma assisted pulsed laser deposition technique. A systematic investigation of the MgO thin films was performed by X-ray diffraction and atomic force microscopy, along with the current-voltage characteristics. A distinguished behavior was observed that the preferred MgO orientation changes from (111) to (001) in the films as the growth temperature increases. Two completely different in-plane epitaxial relationships were also determined from X-ray diffraction as: [110]MgO//[[formula]]Al: ZnO and [110]MgO//[[formula]]Al: ZnO for (001) MgO with 60° rotated triplet domains, and [110]MgO//[[formula]]Al: ZnO for (111) MgO with 180° rotated twin. The pronounced temperature dependence indicates a reconciliation of the nucleation driving forces among surface, interfacial, and strain energy for heteroepitaxy of cubic MgO on hexagonal Al: ZnO. The related interfacial atomic registry is considered to be important to the formation of unusual (001) MgO on hexagonal crystals. In addition, the electrical characterization revealed a dramatic reduction of the leakage current in (001) MgO thin films, whereas the small grain size of (111) MgO is identified by atomic force microscopy as a main cause of large leakage current. [ABSTRACT FROM AUTHOR]

Model evaluations of field-dependent leakage currents in the high-k dielectric oxides HfO2 and ZrO2 are presented. The treatment includes a number of competing transport processes on an equal footing. Our simulation results show that trap-assisted-tunneling, though important, is not the most significant contributor. The combined Poole-Frenkel mechanism with modifications from inelastic trap-related processes dominates at electric fields above 1.5 MV/cm. Our model predictions compare very favorably against the reported experimental data for both HfO2 and ZrO2. Finally, results obtained from the density functional theory based castep simulator are suggestive of dynamic changes in the net energy levels and the possible formation of a mini-band due to oxygen vacancies. [ABSTRACT FROM AUTHOR]

Here, we report the magnetic, ferroelectric, dielectric properties, and Raman spectroscopic studies of multiferroic [(1-x)Pb(Fe0.5Nb0.5)O3-xNi0.65Zn0.35Fe2O4] composites at room temperature. The phase formation of composites was confirmed independently from the X-ray diffraction and Raman studies. The room temperature magnetic studies reveal ferromagnetic like behavior of these composites in contrast to the paramagnetic nature of Pb(Fe0.5Nb0.5)O3. Furthermore, with increasing x, the saturation magnetization, remnant magnetization, and coercive fields are found to increase. The electrical characterizations of these composites reveal a decrease in remnant polarization and dielectric constant with increasing x. More importantly, the x = 0.2 composite is found to be a very good multiferroic material at room temperature among the composites and could be a potential candidate for future potential applications. [ABSTRACT FROM AUTHOR]

ZnS quantum dots (QDs) with cubic phase have been prepared by mechanical alloying the stoichiometric mixture of Zn and S powders at room temperature in a planetary ball mill under Ar. Initially, an amorphouslike thin wurtzite (hexagonal) shell is formed on major zinc-blende (cubic) core after 3.5 h of milling and, in the course of milling up to 20 h, strain free single phase (cubic) QDs are formed with ∼4.5 nm in size. These ball-milled QDs contain different kinds of stacking faults and the Rietveld analysis of x-ray powder diffraction data reveals their concentration in milled samples. Though the high resolution transmission electron microscope (HRTEM) images could not detect the presence of the wurtzite phase but confirm the presence of cubic phase, core-shell structure, and different kinds of stacking faults in ball-milled samples. The particle size of QDs and their distributions obtained from Rietveld analysis agree well with the observations of HRTEM images. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of Bi0.90La0.10(Fe1-xMnx)O3 (x=0, 0.05, 0.10, 0.15, and 0.20) were prepared using a novel mechanical activation followed by a conventional solid-state reaction technique. The formation of the desired materials was confirmed using x-ray diffraction. The electrical and magnetic properties of the materials were investigated at different Mn concentrations as a function of temperature. Both dielectric constant and loss tangent increased with the increase in Mn content in the system. The grain and grain boundary contributions have been estimated using impedance spectroscopy analysis. Both grain and grain boundary conductivity increased with a rise in temperature for all Mn concentrations. The value of activation energy for both grain and grain boundary is nearly the same, and decreased with an increase in Mn concentration. There is a systematic increase in the value of magnetization on increasing Mn concentration. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of Bi0.90La0.10(Fe1-xMnx)O3 (x=0, 0.05, 0.10, 0.15, and 0.20) were prepared using a novel mechanical activation followed by a conventional solid-state reaction technique. The formation of the desired materials was confirmed using x-ray diffraction. The electrical and magnetic properties of the materials were investigated at different Mn concentrations as a function of temperature. Both dielectric constant and loss tangent increased with the increase in Mn content in the system. The grain and grain boundary contributions have been estimated using impedance spectroscopy analysis. Both grain and grain boundary conductivity increased with a rise in temperature for all Mn concentrations. The value of activation energy for both grain and grain boundary is nearly the same, and decreased with an increase in Mn concentration. There is a systematic increase in the value of magnetization on increasing Mn concentration. [ABSTRACT FROM AUTHOR]

La0.60Sr0.40MnO3 (LSMO) thin films of varying thickness from 12 to 55 nm were deposited using the pulsed-laser deposition technique onto single-crystalline SrTiO3 (STO) and STO-buffered Si substrates. The Tc of LSMO films grown on STO-buffered Si substrates decreases faster than films directly grown on STO with decreasing film thickness. The LSMO/STO film with thickness of 55 nm shows Tc at about 360 K, which is close to the bulk value, whereas Tc LSMO film on STO-buffered Si film of similar thickness is reduced to 320 K. This difference is attributed to the strain and interfacial disorders in LSMO film on STO/Si. The film surface morphology is influenced by the film thickness. Oxygenation of LSMO films on STO-buffered Si affects the Tc minimally but improved the overall magnetization of the films due to better oxygenation, which is also the case for postannealing the sample at elevated temperatures. The thermomagnetic history effects observed in LSMO films of STO-buffered Si indicate the presence of inhomogeneity, mostly at the interface, which influences the magnetic properties significantly. [ABSTRACT FROM AUTHOR]

The three-dimensional structure of oleic acid-capped CdSe and thiol-capped CdTe nanocrystals used as quantum dots has been determined by total synchrotron radiation x-ray diffraction and atomic pair distribution function analysis. Both CdSe and CdTe are found to exhibit the zinc-blende-type atomic ordering. It is only slightly distorted in CdSe implying the presence of nanosize domains and very heavily distorted in CdTe due to the presence of distinct core-shell regions. The results well demonstrate the great potential of the experimental approach and thus encourage its wider application in quantum dot research. [ABSTRACT FROM AUTHOR]

Mechanical milling and subsequent annealing in air at temperatures between 210 and 1200 °C have been carried out on high purity ZnO powder to study the defect generation and recovery in the material. Lowering of average grain size (from 76±1 to 22±0.5 nm) as a result of milling has been estimated from the broadening of x-ray lines. Substantial grain growth in the milled sample occurs above 425 °C annealing temperature. Positron annihilation lifetime (PAL) analysis of the samples shows a distinct decrease of the average lifetime of positrons very near the same temperature zone. As indicated from both x-ray diffraction (XRD) and PAL results, high temperature (>700 °C) annealed samples have a better crystallinity (or lower defect concentration) than even the nonmilled ZnO. In contrast, the measured optical band gap of the samples (from absorption spectroscopy) does not confirm lowering of defects with high temperature annealing. Thermally generated defects at oxygen sites cause significant modification of the optical absorption; however, they are not efficient traps for positrons. Different thermal stages of generation and recovery of cationic as well as anionic defects in granular ZnO are discussed in the light of XRD, PAL, and optical absorption studies. [ABSTRACT FROM AUTHOR]

The polycrystalline nanosize (∼60 nm) of (1-x)Pb(Fe2/3W1/3)O3–x(BiFeO3) solid solutions with a wide range of concentrations (0<=x<=0.20) were fabricated using a mechanical activation followed by a conventional solid-state reaction technique. The formation of single-phase material and better solubility of two phases [i.e., BiFeO3 (BFO) and Pb(Fe2/3W1/3)O3 (PFW)] were confirmed using an x-ray diffraction technique. Studies of frequency and temperature dependences of dielectric parameters of solid solutions have provided unique relaxor characteristics of PFW on substitution of a critical composition (i.e., 10%) of BFO in it. The loss tangent (tan δ) peaks of PFW are frequency dependent above room temperature. The sharp tan δ peaks of PFW diffuse on increasing BFO content in PFW–BFO solid solution. This exhibits the induction of relaxation properties in the nonrelaxor PFW material. An ac conductivity (σac) of solid solutions is very much dependent on the frequency and temperature. The nature of temperature dependent conductivity and values of activation energies suggest that space charge and oxygen ion vacancies play an important role in the conduction mechanism in the material. [ABSTRACT FROM AUTHOR]

We report on the magnetic properties of epitaxial La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3 films on Si (100) and Si (111) substrates using SrTiO3 template layer, which demonstrate magnetic and electrical properties at and above room temperature. The magnetization data show magnetic transition and magnetic hysteresis at and above room room temperature. The films show well-defined magnetic domains. The ferromagnetic resonance studies show anisotropic effects related to ferromagnetic properties of films. The smaller grain size of about 20 nm in manganite films on SrTiO3/Si may be one of the reasons to minimize the strain effect through strain relaxation at the interface between SrTiO3 and manganites through the formation of three-dimensonal islands. [ABSTRACT FROM AUTHOR]

We have reported the structural, thermal, microscopic, magnetization, polarization, and dielectric properties of BiFeO3 ceramics synthesized by a rapid liquid-phase sintering technique. Optimum conditions for the synthesis of single-phase BiFeO3 ceramics were obtained. Temperature-dependent magnetization and hysteresis loops indicate antiferromagnetic behavior in BiFeO3 at room temperature. Although saturated ferroelectric hysteresis loops were observed in single-phase BiFeO3 ceramic synthesized at 880 °C, the reduced polarization is found to be due to the high loss and low dielectric permittivity of the ceramic, which is caused by higher leakage current. [ABSTRACT FROM AUTHOR]

We have reported the structural, thermal, microscopic, magnetization, polarization, and dielectric properties of BiFeO3 ceramics synthesized by a rapid liquid-phase sintering technique. Optimum conditions for the synthesis of single-phase BiFeO3 ceramics were obtained. Temperature-dependent magnetization and hysteresis loops indicate antiferromagnetic behavior in BiFeO3 at room temperature. Although saturated ferroelectric hysteresis loops were observed in single-phase BiFeO3 ceramic synthesized at 880 °C, the reduced polarization is found to be due to the high loss and low dielectric permittivity of the ceramic, which is caused by higher leakage current. [ABSTRACT FROM AUTHOR]

Iron-ion-doped barium titanate (BaTiO3) nanoparticles have been synthesized through a chemical route using polyvinyl alcohol. The polymer serves as a surfactant to encapsulate the cationic species in divided groups during the reaction that confines the size and morphology of the specimen. The concentration of Fe3+ varies from 0 to 2 mol % in the specimens. The results from x-ray diffractograms and transmission electron micrographs show that the particle diameters in the specimen lie in the range 29 to 49 nm. It is seen that the ferroelectric-paraelectric phase transition temperature (Tc) varies with the composition and the dielectric permittivity in doped specimens is enhanced by an order of magnitude compared to undoped barium titanate ceramics. The dielectric permittivity shows maxima in the specimen containing 0.3 mol % of dopant concentration. The dielectric behavior of the specimens is explained in terms of the change in crystalline structure of the specimens. [ABSTRACT FROM AUTHOR]

We report on the fabrication of highly epitaxial Y2O3:Eu3+ and Lu2O3:Eu3+ films on sapphire and Si single crystalline, and quartz substrates under different growth and optimization conditions using pulsed-laser deposition technique. The films were characterized using x rays, microstructure, and spectroscopic measurements. Our results demonstrate superior spectroscopic performance on the films grown on sapphire substrates due to the high quality and epitaxial nature of the film. The surface morphology of the epitaxial films controls the photoluminescence property of these phosphors film. [ABSTRACT FROM AUTHOR]

Ti-doped MgB[sub 2]/Cu tapes with Ta as a buffer layer were prepared through the in situ powder in tube method by using Mg, Ti, and B powders. The phase compositions, microstructure features, and superconducting properties were investigated by x-ray diffraction, scanning electron microscope, and superconducting quantum interference device magnetometer. It is found that TiB[sub 2] phase was formed in Ti-doped MgB[sub 2] tape. Magnetization measurement results show that the critical transition temperature of MgB[sub 2]/Ta/Cu tape with Ti doping is around 38 K. The irreversibility field H[sub irr] and critical current density J[sub c] can be greatly enhanced by Ti doping. H[sub irr] of the Mg[sub 0.9]Ti[sub 0.1]B[sub 2] tape is as high as 7.4 T at 10 K. The high critical current density J[sub c] of 1.5 × 10[sup 6] A/cm² (10 K, self field) and 9.3 × 10[sup 5] A/cm² (20 K, self field) are obtained in the Mg[sub 0.9]Ti[sub 0.1]B[sub 2] tape. In addition, a suitable amount of Ti doping can lead to a high density and fine grain size of MgB[sub 2], which may be the reason for high J[sub c] in Ti-doped MgB[sub 2] tapes. [ABSTRACT FROM AUTHOR]

We prepared a series of Mg[sub 1-χ]Zr[sub χ]B[sub 2] bulk samples with different x values by the solid-state reaction at ambient pressure and investigated the effects of the Zr doping on phase compositions, microstructure, and flux pinning behavior. The results indicate that the a axis increases with the increase of the Zr doping and the c axis remains unchanged. ZrB[sub 2] phases form and a small amount of Zr atoms may substitute Mg in Zr-doped samples. Critical temperature drops with increasing the Zr doping. It is found that critical current density J[sub c] can be significantly enhanced by the Zr doping and the best data are achieved in Mg[sub 0.9]Zr[sub 0.1]B[sub 2]. For this sample, J[sub c] values are remarkably improved to 1.83 × 10[sup 6] A/cm² in the self field and 5.51 × 10[sup 5] A/cm² in 1 T at 20 K. Also, the irreversibility field is increased by the Zr doping. The high density, fine grain size of MgB[sub 2], and small ZrB[sub 2] particles in Zr-doped samples may be responsible for the enhancement of J[sub c]. Also, the field dependence of J[sub c] at different temperatures was briefly discussed. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of [Bi.sub.0.90][La.sub.0.10]([Fe.sub.1-x][Mn.sub.x])[O.sub.x] are prepared by using a mechanical activation followed by a conventional solid-state reaction method and their electric and magnetic properties at different Mn concentrations are examined. Grain and grain boundary conductivity has increased with a rise in temperature for all Mn concentrations and there is a systematic increase in the value of magnetization on increasing Mn concentration.