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The structural, magnetic, ferroelectric, and magnetoelectric (ME) properties of lead-free ferroelectric phase (0.45)Ba0.7Ca0.3TiO3-(0.55)BaTi0.8Zr0.2O3 (BCZT) and rare earth modified Co-Mn ferrite phase Co0.7Mn0.3Fe1.95Dy0.05O4 (CMFDO) magnetoelectric (ME) composites are reported. X-ray diffraction confirms the presence of a crystal structure corresponding to both the ferroelectric and ferrite phases, which was further confirmed by Raman spectroscopic measurements. Scanning electron micrograph imaging along with the elemental mapping reveals the distribution of CMFDO grains in a BCZT matrix. The variation of dc resistivity with temperature indicates a semiconducting nature of the ME composite. The ME composite shows usual dielectric dispersion behavior with a higher dielectric constant value in the low frequency region compared to the individual ferroic phases, due to the space charge effects. Frequency dependent ac conductivity reveals that the conduction process in the ME composite is due to the small polaron hopping mechanism. Also, the variation of dielectric constant with temperature reveals the presence of two dielectric anomalies corresponding to ferroelectric phase transitions, i.e., from orthorhombic (O) to tetragonal (T) phases (∼298–323 K) and tetragonal (T) to cubic (C) phases (∼400 K). The ME composite exhibits both the ferroelectric [i.e., polarization (P) vs electric field (E)] and ferrimagnetic [i.e., magnetization (M) vs magnetic field (H)] hysteresis loops that confirm its multiferroic nature. The P-E hysteresis loop indicates the significant changes in remanent polarization (ΔPr ∼ 54%) after magnetic poling, confirming the presence of strong magnetoelectric coupling in the ME composite. Further, the strength of the ME coupling calculated was ∼54%, which is remarkable. Thus, the ME composite prepared in the present study may be a suitable candidate for applications in magnetic field sensors and multistate memory devices and may be suitable alternatives for single phase multiferroics. [ABSTRACT FROM AUTHOR]

The present study explores the effect of Dy3+ rare-earth ion substitution on the crystal structure, morphology, and magnetic properties of magnetostrictive Co0.7Mn0.3Fe2O4 spinel ferrite and demonstrates their potential applications in magnetomechanical sensors. The intrinsic CoFe2O4 and Dy-substituted Co0.7Mn0.3Fe2−xDyxO4 (x = 0.0–0.1) were prepared by the standard solid-state chemical reaction method. X-ray diffraction studies along with the Rietveld refinement confirm that all the samples exhibit single-phase cubic spinel structure with space group Fd 3 ¯ m. Raman and Mössbauer data analyses reveal that the cation redistribution with Mn and Dy cosubstitution in CoFe2O4 and confirm the presence of a mixed spinel structure. Electron microscopy analysis indicates the significant effect of Mn, Dy cosubstitution on the microstructure of CoFe2O4. All the samples exhibit the magnetic hysteresis (M-H) loops at 5 K and 300 K. Saturation magnetization (Ms) and the cubic anisotropy constant (K1) values increase with Mn substitution, while with Dy substitution, Ms reduces due to the decrease of magnetic interactions with Dy substitution. However, the coercive field decreases with Mn and increases with Dy substitution. Higher values of magnetostriction coefficients (λ11 = −95 ppm and λ12 = 52 ppm) and the strain derivative (d λ / d H = 0.075 ppm / Oe at 600 Oe) observed make Co0.7Mn0.3Fe1.95Dy0.05O4 a suitable candidate for designing torque/stress sensors and a magnetostrictive phase for making magnetoelectric composite. Chemical composition optimization yields higher values Ms (89 emu/g, i.e., 3.73 μB) at lower coercivity (Hc = 241 Oe) for Co0.7Mn0.3Fe2O4 and higher values of λ11, λ12, and d λ / d H at a lower magnetic field (below 800 Oe) for Co0.7Mn0.3Fe1.95Dy0.05O4. The results suggest and demonstrate that Co0.7Mn0.3Fe2O4 and Co0.7Mn0.3Fe1.95Dy0.05O4 are the potential candidates for designing magnetomechanical sensor applications. [ABSTRACT FROM AUTHOR]

Thin (40–150 nm), highly doped n+ (1019–1020 cm−3) Ga2O3 layers deposited using pulsed laser deposition (PLD) were incorporated into Ti/Au ohmic contacts on (001) and (010) β-Ga2O3 substrates with carrier concentrations between 2.5 and 5.1 × 1018 cm−3. Specific contact resistivity values were calculated for contact structures both without and with a PLD layer having different thicknesses up to 150 nm. With the exception of a 40 nm PLD layer on the (001) substrate, the specific contact resistivity values decreased with increasing PLD layer thickness: up to 8× on (001) Ga2O3 and up to 16× on (010) Ga2O3 compared with samples without a PLD layer. The lowest average specific contact resistivities were achieved with 150 nm PLD layers: 3.48 × 10−5 Ω cm2 on (001) Ga2O3 and 4.79 × 10−5 Ω cm2 on (010) Ga2O3. Cross-sectional transmission electron microscopy images revealed differences in the microstructure and morphology of the PLD layers on the different substrate orientations. This study describes a low-temperature process that could be used to reduce the contact resistance in Ga2O3 devices. [ABSTRACT FROM AUTHOR]

We report on the combined experimental and theoretical simulation results of lead-free ferroelectrics, Ba(1-x)CaxTiO3 (x =0.0–0.3) and BaTi(1-y)ZryO3 (y =0.0–0.2), synthesized by standard solid state reaction method. First principles density functional calculations are used to investigate the electronic structure, dynamical charges, and spontaneous polarization of these compounds. In addition, the structural, ferroelectric, piezoelectric, and dielectric properties are studied using extensive experiments. The X-ray diffraction and temperature dependent Raman spectroscopy studies indicate that the calcium (Ca) substituted compositions exhibit a single phase crystal structure, while zirconium (Zr) substituted compositions are biphasic. The scanning electron micrographs reveal the uniform and highly dense microstructure. The presence of polarization-electric field and strain-electric field hysteresis loops confirms the ferroelectric and piezoelectric nature of all the compositions. Our results demonstrate higher values for polarization, percentage strain, piezoelectric coefficients, and electrostrictive coefficient compared to those existing in the literature. For smaller substitutions of Ca and Zr in BaTiO3, a direct piezoelectric coefficient (d33) is enhanced, while the highest d33 value (∼300 pC/N) is observed for BaTi0.96Zr0.04O3 due to the biphasic ferroelectric behavior. Calculation of Born effective charges indicates that doping with Ca or Zr increases the dynamical charges on Ti as well as on O and decreases the dynamical charge on Ba. An increase in the dynamical charges on Ti and O is ascribed to the increase in covalency of Ti-O bond that reduces the polarizability of the crystal. A broader range of temperatures is demonstrated to realize the stable phase in the Ca substituted compounds. The results indicate enhancement in the temperature range of applicability of these compounds for device applications. The combined theoretical and experimental study is expected to enhance the current scientific understanding of the lead-free ferroelectric materials. [ABSTRACT FROM AUTHOR]

Realization of high temperature physical measurement sensors, which are needed in many of the current and emerging technologies, is challenging due to the degradation of their electrical stability by drift currents, material oxidation, thermal strain, and creep. In this paper, for the first time, we demonstrate that 3D printed sensors show a metamaterial-like behavior, resulting in superior performance such as high sensitivity, low thermal strain, and enhanced thermal stability. The sensors were fabricated using silver (Ag) nanoparticles (NPs), using an advanced Aerosol Jet based additive printing method followed by thermal sintering. The sensors were tested under cyclic strain up to a temperature of 500 °C and showed a gauge factor of 3.15 ± 0.086, which is about 57% higher than that of those available commercially. The sensor thermal strain was also an order of magnitude lower than that of commercial gages for operation up to a temperature of 500 °C. An analytical model was developed to account for the enhanced performance of such printed sensors based on enhanced lateral contraction of the NP films due to the porosity, a behavior akin to cellular metamaterials. The results demonstrate the potential of 3D printing technology as a pathway to realize highly stable and high-performance sensors for high temperature applications. [ABSTRACT FROM AUTHOR]

We report on the enhanced magnetostrictive properties of nanocrystalline Dysprosium (Dy3+) substituted iron-rich cobalt ferrites (Co0.8Fe(2.2-x)DyxO4, referred to as CFDO). The CFDO samples with a variable Dy concentration (x = 0.000–0.075) were synthesized by the sol-gel auto-combustion method. The phase purity and crystal structure were confirmed from X-ray diffraction analyses coupled with Rietveld refinement. Surface morphology analysis using scanning electron microscopy imaging indicates the agglomerated magnetic particles with a non-uniform particle size distribution, which is desirable to transfer the strain. The magnetostriction coefficient (λ11) measurements indicate that the CFDO with Dy concentration x = 0.025 exhibits the highest strain sensitivity, (dλ/dH) ∼1.432 nm/A (for H ≤ 1000 Oe). On the other hand, the magnetostriction coefficient (λ12) measurements indicate that the Dy concentration x = 0.075 exhibits the larger (dλ/dH) ∼ 0.615 nm/A (for H ≤ 1000 Oe). The maximum λ11value of 166 ppm (at H = 3300 Oe) was observed for a compound with Dy concentration x = 0.050. Magnetization measurements indicate that the saturation magnetization and coercivity of CFDO samples are dependent on the Dy3+content; the highest value of squareness ratio of 0.424 was observed for x = 0.050. The interplay between strain sensitivity (dλ/dH) and instantaneous susceptibility (dM/dH), as derived from magnetostriction and magnetization results, demonstrates that these CFDO materials may be useful for developing torque/stress sensors, as a constituent magnetostrictive phase for making the magnetoelectric composite materials and thus suitable for magnetoelectric sensor applications. [ABSTRACT FROM AUTHOR]

Printed electronics has emerged as a versatile eco-friendly fabrication technique to create sintered nanoparticle (NP) films on arbitrary surfaces with an excellent control over the film microstructure. While applicability of such films for high-temperature applications is not explored previously, herein we report the high-temperature electrical stability of silver (Ag) metal NP films fabricated using an Aerosol Jet based printing technique and demonstrate that this behavior is dictated by changes in the film microstructure. In-situ high temperature (24-500 °C) impedance spectroscopy measurements show that the real part of the impedance increases with increasing temperature up to 150 ° C, at which point a decreasing trend prevails until 300 ° C, followed again by an increase in impedance. The electrical behavior is correlated with the in-situ grain growth of the Ag NP films, as observed afterwards by scanning electron microscopy and X-ray diffraction (XRD), and could be tailored by controlling the initial microstructure through sintering conditions. Using combined diffraction and spectroscopic analytical methods, it is demonstrated the Aerosol Jet printed Ag NP films exhibit enhanced thermal stability and oxidation resistance. In addition to establishing the conditions for stability of Ag NP films, the results provide a fundamental understanding of the effect of grain growth and reduction in grain boundary area on the electrical stability of sintered NP films. [ABSTRACT FROM AUTHOR]

Gadolinium (Gd) substituted cobalt ferrites (CoFe2-xGdxO4, referred to CFGO) with variable Gd content (x=0.0-0.4) have been synthesized by solid state ceramic method. The crystal structure and impedance properties of CFGO compounds have been evaluated. X-ray diffraction measurements indicate that CFGO crystallize in the inverse spinel phase. The CFGO compounds exhibit lattice expansion due to substitution of larger Gd ions into the crystal lattice. Impedance spectroscopy analysis was performed under a wide range of frequency (f=20 Hz-1 MHz) and temperature (T=303-573 K). Electrical properties of Gd incorporated Co ferrite ceramics are enhanced compared to pure CoFe2O4 due to the lattice distortion. Impedance spectroscopic analysis illustrates the variation of bulk grain and grain-boundary contributions towards the electrical resistance and capacitance of CFGO materials with temperature. A two-layer heterogeneous model consisting of moderately conducting grain interior (ferrite-phase) regions separated by insulating grain boundaries (resistive-phase) accurately account for the observed temperature and frequency dependent electrical characteristic of CFGO ceramics. [ABSTRACT FROM AUTHOR]

We report on the ferroelectricity for morphotropic-phase-boundary lead (Pb) free 0.5BaTi0.8Zr0.2 O3-0.5Ba0.7Ca0.3TiO3 (0.5BZT-0.5BCT) thin films. Thin films were grown on Pt/Ti/SiO2/Si substrate using pulsed laser deposition. Raman spectroscopic data combined with the X-ray diffraction analyses confirm body centered tetragonal crystallographic structure 0.5BZT-0.5 BCT thin films on Pt/Ti/SiO2/Si. Polarization studies demonstrate that these 0.5BZT-0.5BCT films exhibit a large remnant and saturation polarization of 37 μC/cm2 and 40 μC/cm2, respectively, with a coercive field of 140 kV/cm. A correlation between polarization dynamics, structural distortion, and phonon vibration is established. The splitting of X-ray diffraction peak of the thin film in the 2θ range of 44.5° to 46.5° represents high degree of tetragonality. The tetragonality factor calculated by Rietveld analysis was found to be 0.006 and can be a major cause for the increased remnant polarization value. It is established from Raman spectra that the non-centrosymmetricity due to the displacement of Ti/Zr ions from its octahedral position is related to the peak position as well as the broadening of the A1 (LO) optical phonon mode. This increase of broadness in the thin film causes an increase in the dipole moment of the unit cell and, hence, the net increase in polarization values. [ABSTRACT FROM AUTHOR]

Manganese (Mn) substituted cobalt ferrites (CoFe2-xMnxO4, referred to CFMO) have been synthesized by the solid state reaction method and their dielectric properties and ac conductivity have been evaluated as a function of applied frequency and temperature. X-ray diffraction measurements indicate that CFMO crystallize in the inverse cubic spinel phase with a lattice constant ∼8.3 8Å. Frequency dependent dielectric measurements at room temperature obey the modified Debye model with relaxation time of 10-4 s and spreading factor of 0.35(±0.05). The frequency (20 Hz-1MHz) and temperature (T=300-900 K) dependent dielectric constant analyses indicate that CFMO exhibit two dielectric relaxations at lower frequencies (1-10 kHz), while completely single dielectric relaxation for higher frequencies (100 kHz-1 MHz). The dielectric constant of CFMO is T-independent up to ∼400 K, at which point increasing trend prevails. The dielectric constant increase with T>400K is explained through impedance spectroscopy assuming a two-layer model, where low-resistive grains separated from each other by high-resistive grain boundaries. Following this model, the two electrical responses in impedance formalism are attributed to the grain and grain-boundary effects, respectively, which also satisfactorily accounts for the two dielectric relaxations. The capacitance of the bulk of the grain determined from impedance analyses is ∼10 pF, which remains constant with T, while the grain-boundary capacitance increases up to ∼3.5 nF with increasing T. The tan δ (loss tangent)-T also reveals the typical behavior of relaxation losses in CFMO. [ABSTRACT FROM AUTHOR]

Titanium (Ti) doped tungsten oxide (WO3) thin films were grown by co-sputter deposition of W and Ti metal targets. The sputtering powers to the W and Ti were kept constant at 100W and 50 W, respectively, while varying the growth temperature (Ts) in the range of 25-400 °C. The structural quality of Ti-doped WO3 films is dependent on Ts. Ti-doped WO3 films grown at Ts<400 °C were amorphous. A temperature of 400 °C is critical to promote the structural order and formation of monoclinic, nanocrystalline films. The optical constants and their dispersion profiles determined from spectroscopic ellipsometry indicate that there is no significant inter-diffusion at the film-substrate interface for W-Ti oxide film growth of ∼40 nm. The index refraction (n) at λ=550 nm varies in the range of 2.15-2.40 with a gradual increase in Ts. Lorentz-Lorenz analysis (n(λ)=550 nm) of the data indicates the gradual improvement in the packing density coupled with structural transformation accounts for the observed optical quality of the Ti-doped WO3 films as a function of Ts. A correlation between the growth conditions and optical constants is discussed. [ABSTRACT FROM AUTHOR]

Gallium oxide (Ga2O3) thin films were made by sputter deposition employing a Ga2O3 ceramic target for sputtering. The depositions were made over a wide range of substrate temperatures (Ts), from 25 to 600 °C. The effect of Ts on the chemical bonding, surface morphological characteristics, optical constants, and electrical properties of the grown films was evaluated using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and four-point probe measurements. XPS analyses indicate the binding energies (BE) of the Ga 2p doublet, i.e., the Ga 2p3/2 and Ga 2p1/2 peaks, are located at 1118.0 and 1145.0 eV, respectively, characterizing gallium in its highest chemical oxidation state (Ga3+) in the grown films. The core level XPS spectra of O 1s indicate that the peak is centered at a BE~531 eV, which is also characteristic of Ga-O bonds in the Ga2O3 phase. The granular morphology of the nanocrystalline Ga2O3 films was evident from AFM measurements, which also indicate that the surface roughness of the films increases from 0.5 nm to 3.0 nm with increasing Ts. The SE analyses indicate that the index of refraction (n) of Ga2O3 films increases with increasing Ts due to improved structural quality and packing density of the films. The n(k) of all the Ga2O3 films follows the Cauchy's dispersion relation. The room temperature electrical resistivity was high (~200 Ω-cm) for amorphous Ga2O3 films grown at Ts RT-300 °C and decreased to ~1 Ω-cm for nanocrystalline Ga2O3 films grown at Ts500-600 °C. A correlation between growth conditions, microstructure, optical constants, and electrical properties of Ga2O3 films is derived. [ABSTRACT FROM AUTHOR]

Manganese (Mn) substituted cobalt ferrites (CoFe2-xMnxO4, referred to CFMO) were synthesized and their structural, magnetic, and dielectric properties were evaluated. X-ray diffraction measurements coupled with Rietveld refinement indicate that the CFMO materials crystallize in the inverse cubic spinel phase. Temperature (T = 300 K and 10 K) dependent magnetization (M(H)) measurements indicate the long range ferromagnetic ordering in CoFe2-xMnxO4 (x = 0.00-0.15) ferrites. The cubic anisotropy constant (K1(T)) and saturation magnetization (Ms(T)) were derived by using the 'law of approach' to saturation that describes the field dependence of M(H) for magnetic fields much higher than the coercive field (Hc). Saturation magnetization (Ms), obtained from the model, decreases with increasing temperature. For CoFe2O4, Ms decreases from 3.63 μB per formula unit (f.u.) to 3.47 μB/f.u. with increasing temperature from 10 to 300 K. CFMO (0.00-0.15) exhibit the similar trend while the magnitude of Ms is dependent on Mn-concentration. Ms-T functional relationship obeys the Bloch's law. The lattice parameter and magnetic moment calculated for CFMO reveals that Mn ions occupying the Fe and Co position at the octahedral site in the inverse cubic spinel phase. The structure and magnetism in CFMO are further corroborated by bond length and bond angle calculations. The dielectric constant dispersion of CFMO in the frequency range of 20 Hz-1 MHz fits to the modified Debye's function with more than one ion contributing to the relaxation. The relaxation time and spread factor derived from modeling the experimental data are ∼10-4 s and ∼0.35(±0.05), respectively. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties of lithium iron pyrophosphate, i.e., Li2Fe3(P2O7)2 or LiFe1.5P2O7, synthesized using a facile metal acetate approach for application in lithium-ion batteries, are investigated in detail. The high-resolution transmission electron microscopy, selected area electron diffraction, and x-ray diffraction measurements indicate that Li2Fe3(P2O7)2 is crystallized in the monoclinic structure, without any indication of crystallographic defects such as dislocations or misfits, and exhibit smooth surface morphology. The evaluated lattice parameters are a=0.698 76 nm, b=0.812 36 nm, c=0.964 22 nm, and β=111.83° (P21/c space group). Infrared spectroscopic measurements indicate the presence of P2O7 groups, which are formed by the two PO4 tetrahedral groups connected together. The magnetic measurements indicate that Li2Fe3(P2O7)2 is a weak antiferromagnetic material with TN=20 K exhibiting a Curie constant Cp=3.38 emu K/mol per Fe ion and a negative value of the Weiss temperature (Θp=-15 K). The absence of higher valence state Fe impurities and antiferromagnetic interactions due to the greater distance between two equivalent magnetic ions, which vanishes the Fe–O–Fe superexchange interactions, is confirmed. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties of lithium iron pyrophosphate, i.e., Li2Fe3(P2O7)2 or LiFe1.5P2O7, synthesized using a facile metal acetate approach for application in lithium-ion batteries, are investigated in detail. The high-resolution transmission electron microscopy, selected area electron diffraction, and x-ray diffraction measurements indicate that Li2Fe3(P2O7)2 is crystallized in the monoclinic structure, without any indication of crystallographic defects such as dislocations or misfits, and exhibit smooth surface morphology. The evaluated lattice parameters are a=0.698 76 nm, b=0.812 36 nm, c=0.964 22 nm, and β=111.83° (P21/c space group). Infrared spectroscopic measurements indicate the presence of P2O7 groups, which are formed by the two PO4 tetrahedral groups connected together. The magnetic measurements indicate that Li2Fe3(P2O7)2 is a weak antiferromagnetic material with TN=20 K exhibiting a Curie constant Cp=3.38 emu K/mol per Fe ion and a negative value of the Weiss temperature (Θp=-15 K). The absence of higher valence state Fe impurities and antiferromagnetic interactions due to the greater distance between two equivalent magnetic ions, which vanishes the Fe–O–Fe superexchange interactions, is confirmed. [ABSTRACT FROM AUTHOR]

Structural and electronic characteristics of KY(WO4)2 (KYW) (010) crystal surfaces have been studied using reflection high-energy electron diffraction (RHEED) and x-ray photoelectron spectroscopy (XPS). The results indicate that the crystal structure and chemical composition of the mechanically polished pristine surface is stoichiometrically well maintained as expected for KYW crystals. Combined measurements of RHEED and XPS as a function of 1.5 keV Ar+ ion irradiation of the KYW (010) surfaces indicate amorphization, partial loss of potassium atoms, and partial transformation of chemical valence state of tungsten from W6+ to a lower valence state, W0 state predominantly, which induces electronic states at the top of valence band. [ABSTRACT FROM AUTHOR]

Multiphoton ionization spectroscopy is used to characterize the (3sσ) 3Πg Rydberg state of O2. It is found that the 3Πg Rydberg state is very diffuse and has rotationally resolved structure for the v’=2 level only. The FWHM of rotational lines for both the (3sσ) 3,1Πg states is greater than the excitation bandwidth, indicating strong radiationless decay of the two states. Interactions with the nearby 3Πg and 1Πg valence states are invoked to explain the observed behavior. [ABSTRACT FROM AUTHOR]

We report the magnetic and electron spin resonance (ESR) properties of W doped CoFe2O4 polycrystalline materials, prepared by standard solid-state reaction method. W was doped (0-15%) in CFO lattice on Fe site. Isothermal magnetization measurements reveal that the coercive field (Hc) (1300-2200 Oe) and saturation magnetization MS (35-82 emu/g) vary strongly as a function of W doping at all the temperatures (4-300 K) measured. We believe that a strong decrease in magnetic anisotropy in CFO after doping with W could cause a decrease in Hc. Up on doping CFO with W in place of Fe, the process transforms part of Fe3+ into Fe2+ due to the creation of more oxygen vacancies. This hinders the super-exchange interaction between Fe3+ and Fe2+, which causes a decrease in MS. Zero-field cooled (ZFC) and field cooled (FC, 1000 Oe) magnetization responses measured at 4 K on 1% W doped CFO show no indication of exchange bias, inferring that there are no other microscopic secondary magnetic phases (no segregation). This observation is corroborated by ESR (9.398 GHz) measurements collected as a function of temperature (10-150 K) and W doping (0-15%). We find that ESR spectra did not change after doping with W above 0.5%. However, ESR spectra collected from 0.5% W doped CFO sample showed a strong temperature dependence. We observed several ESR signals from 0.5% W doped CFO sample that could be due to phase separation. [ABSTRACT FROM AUTHOR]

The effect of sputtering pressure on the surface/interface microstructure, crystal phase, mechanical properties and electrical characteristics of nanocrystalline W-Mo films is reported. The W-Mo films (≈300 nm) with variable microstructure were deposited under variable argon (Ar) sputtering pressure (PAr), which is varied in the range of 3-19 mTorr. X-ray diffraction analyses indicate that the W-Mo films crystallize in thermodynamically stable α-phase of W. However, the crystal-quality degradation occurs for W-Mo films deposited at higher PAr due to difference in the adatom mobilities. The average grain size (d) of the W-Mo films was in the range of 11-24 nm; grain size decreases with increasing PAr. The effect of PAr and associated microstructure are significant on the mechanical characteristics; the hardness (H) and modulus of elasticity (Er) of W-Mo films deposited at lower PAr were higher but decreases continuously with increasing PAr. The W-Mo films deposited under optimum sputtering pressure exhibit superior mechanical characteristics: H=40 GPa, Er=275 GPa, H/Er=0.8, and H3/Er 2=0.145 GPa, which are higher compared to pure, α-phase W-films. The W-Mo films deposited at PAr=3-9 mTorr exhibit high resistivity≈350-400 μΩ-cm, which decreases to 150-200 μΩ-cm for films deposited at higher PAr. Based on the results, structure-mechanical-electrical property correlation inW-Mo films is established. [ABSTRACT FROM AUTHOR]

We present an approach to design Ga2O3-based materials with tunable optical properties. In the Ti-doped Ga2O3 model system, where the Ti content (x) was varied up to ~5 at. %, Ti induced significant effects on the structural and optical properties. Single-phase b-Ga2O3 formation occurs for a lower Ti content (≥1.5 at. %); however, composite-oxide (Ga2O3-TiO2) formation occurs for a higher Ti content. While band gap reduction (Eg~0.9 eV) coupled with refractive index (n) enhancement occurs, indicating the electronic-structure modification, with Ti incorporation, the changes are dominant only in the Ga2O3-TiO2-composite. A direct, functional Ti(x)-Eg-n relationship was found, which suggests that tailoring the optical quality and performance of Ga-Ti-O is possible by tuning the Ti content and structure. [ABSTRACT FROM AUTHOR]

An approach is presented to increase the toughness (KIC) while retaining high hardness (H) of Zr-W-N nanocrystalline coatings using energetic ions bombardment. Tuning KIC and H values was made possible by a careful control over the substrate bias, i.e., the kinetic energy (Uk∼9-99 J/cm3) of the bombarding ions, while keeping the deposition temperature relatively low (200 °C). Structural and mechanical characterization revealed a maximum wear resistance (H/Er∼0.23) and fracture toughness (KIC∼2.25 MPa √ m) of ZrWN coatings at Uk∼72 J/cm3. A direct Uk-microstructure-KIC-H relationship suggests that tailoring mechanical properties for a given application is possible by tuning Uk and, hence, ZrWN-coatings' microstructure. [ABSTRACT FROM AUTHOR]

Hafnium oxide (HfO2) films were grown by sputter-deposition by varying the growth temperature (Ts=25-700 °). HfO2 films grown at Ts<200 ° were amorphous, while those grown at Ts≤200 ° were monoclinic, nanocrystalline with (111) texturing. X-ray reflectivity (XRR) analyses indicate that the film-density (q) increases with increasing Ts. The index of refraction (n) profiles derived from spectroscopic ellipsometry analyses follow the Cauchy dispersion relation. Lorentz-Lorenz analysis (n(λ)=550 nm) and optical-model adopted agree well with the XRR data/analyses. A direct Ts-q-n relationship suggesTs that tailoring the optical quality is possible by tuning Ts and the microstructure of HfO2 films. [ABSTRACT FROM AUTHOR]

Tungsten (W) incorporated Ga2O3 films were produced by co-sputter deposition. W-concentration was varied by the applied sputtering-power. The structure and optical properties of W-incorporated Ga2O3 films were evaluated using X-ray diffraction, scanning electron microscopy, and spectrophotometric measurements. No secondary phase formation was observed in W-incorporated Ga2O3 films. W-induced effects were significant on the structure and optical properties of Ga2O3 films. The bandgap of Ga2O3 films without W-incorporation was ∼5 eV. Red-shift in the bandgap was noted with increasing W-concentration indicating the electronic structure changes in W-Ga2O3 films. A functional relationship between W-concentration and optical property is discussed. [ABSTRACT FROM AUTHOR]

Lanthanum oxide (La2O3) films were grown by the reactive dc magnetron sputtering and studied their structural, chemical and optical parameters. La2O3 films were deposited onto Si substrates by sputtering La-metal in a reactive gas (Ar+O2) mixture at a substrate temperature of 200 °C. Reflection high-energy electron diffraction measurements confirm the amorphous state of La2O3 films. Chemical analysis of the top-surface layers evaluated with x-ray photoelectron spectroscopy indicates the presence of a layer modified by hydroxylation due to interaction with atmosphere. Optical parameters of a-La2O3 were determined with spectroscopic ellipsometry (SE). There is no optical absorption over spectral range λ=250-1100 nm. Dispersion of refractive index of a-La2O3 was defined by fitting of SE parameters over λ=250-1100 nm. [ABSTRACT FROM AUTHOR]

Inherent processes in coal gasification plants produce hazardous hydrogen sulfide (H2S), which must be continuously and efficiently detected and removed before the fuel is used for power generation. An attempt has been made in this work to fabricate tungsten oxide (WO3) thin films by radio-frequency reactive magnetron-sputter deposition. The impetus being the use of WO3 films for H2S sensors in coal gasification plants. The effect of growth temperature, which is varied in the range of 30–500 °C, on the growth and microstructure of WO3 thin films is investigated. Characterizations made using scanning electron microscopy (SEM) and x-ray diffraction (XRD) indicate that the effect of temperature is significant on the microstructure of WO3 films. XRD and SEM results indicate that the WO3 films grown at room temperature are amorphous, whereas films grown at higher temperatures are nanocrystalline. The average grain-size increases with increasing temperature. WO3 films exhibit smooth morphology at growth temperatures ≤300 °C while relatively rough at >300 °C. The analyses indicate that the nanocrystalline WO3 films grown at 100–300 °C could be the potential candidates for H2S sensor development for application in coal gasification systems. [ABSTRACT FROM AUTHOR]

Nanostructures of Fe oxides and hydroxides with varying morphologies have been prepared in aqueous media by precipitation of iron nitrate and ammonium hydroxide. The approach is based on a simple wet-chemical route involving different solutions of Fe-oxide/hydroxide particles in suspension and acetic acid at different concentrations and subject to heat treatment at 373 K. The growth and structural characteristics have been investigated using x-ray diffraction (XRD) and high-resolution scanning electron microscopy (HRSEM). XRD results indicate that the solids obtained from aqueous stage exhibit goethite [α-FeO(OH)] with average particle size of 2–3 nm, while the samples with acetic acid addition show hematite (α-Fe2O3) with average size of ∼20 nm. HRSEM results confirm the presence of particles of ∼100 nm in samples with no acetic acid, while the samples with acetic acid exhibit nanoparticles of ∼20 nm. The analysis also indicates the presence of net-shaped structures and particles with high-dense porosity within the nanoregime depending on the concentration of acetic acid. Fe-oxide nanoparticles and networks are stable up to a temperature of 773 K. [ABSTRACT FROM AUTHOR]

A simple low-temperature chemical method to produce metastable hexagonal phase molybdenum oxide (h-MoO3) nanorods and their excellent structural characteristics has been demonstrated. In this approach, h-MoO3 samples were prepared by precipitating molybdenum oxide from an ammonium paramolybdate solution by the adding nitric acid. The structure of h-MoO3 nanorods was examined in detail using high-resolution scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM). The SEM data reveal that the nanorod h-MoO3 crystals have the shape of straight hexagonal rods with an aspect ratio ∼60. The HR-TEM results confirm the hexagonal structure of the MoO3 nanocrystals. Computations of the observed TEM data along with x-ray diffraction pattern further confirm the stability of the nanostructure of h-MoO3 rods. [ABSTRACT FROM AUTHOR]

Molybdenum oxide (MoO3) exhibits interesting structural, chemical, electrical, and optical properties, which are dependent on the growth conditions and the fabrication technique. In the present work, MoO3 films were produced by pulsed-laser deposition and dc magnetron sputtering under varying conditions of growth temperature (Ts) and oxygen pressure (pO2). The effect of growth conditions on the structure and chemical properties of MoO3 films was examined using x-ray diffraction, reflection high-energy electron diffraction, x-ray photoelectron spectroscopy, and infrared spectroscopic measurements. The analyses indicate that the microstructure of Mo oxide films is sensitive to Ts and pO2. The growth conditions were optimized to produce stoichiometric and highly textured polycrystalline MoO3 films. A comparison of the microstructure of MoO3 films grown using pulsed-laser deposition and sputtering methods is also presented. [ABSTRACT FROM AUTHOR]

LiNi0.8Co0.15Al0.05O2 films were grown by pulsed-laser deposition (PLD) in the temperature (Ts) range of 30–500 °C and oxygen partial pressure (pO2) maintained in the range of 50–150 mTorr. The grown films were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy (RS), and electrochemical measurements in order to understand their growth behavior, surface morphology, local chemical structure, and electrochemical properties. XRD, RS, and SEM measurements indicate that the growth and microstructure of PLD LiNi0.8Co0.15Al0.05O2 films are highly sensitive to the deposition temperature and reactive atmosphere during laser ablation. The fabrication conditions were optimized to produce device quality LiNi0.8Co0.15Al0.05O2 films for electrochemical applications. The charge-discharge profiles of cells using the PLD grown Li(Ni,Co,Al)O2 films as electrodes demonstrate their applicability in microbatteries. A stable capacity of 98 μA h/cm2 μm was obtained in the potential range of 4.2–2.5 V for LiNi0.8Co0.15Al0.05O2 films grown at 450 °C. [ABSTRACT FROM AUTHOR]

Reports a detailed characterization of the ¹Π[subg] Rydberg state in oxygen. Vibrational component of a rotationally resolved electronic transition in oxygen; Vibrational levels of the ¹Π[subg] state; electron energy loss spectrum of oxygen.

Yttrium oxide (Y2O3) films with an average crystallite-size (L) ranging from 5 to 40 nm were grown by sputter-deposition onto Si(100) substrates. The optical properties of grown Y2O3 films were evaluated using spectroscopic ellipsometry measurements. The size-effects were significant on the optical constants and their dispersion profiles of Y2O3 films. A significant enhancement in the index of refraction (n) is observed in well-defined Y2O3 nanocrystalline films compared to that of amorphous Y2O3. A direct, linear L-n relationship found for Y2O3 films suggests that tuning optical properties for desired applications can be achieved by controlling the size at the nanoscale dimensions. [ABSTRACT FROM AUTHOR]

We report on an ab initio molecular dynamics study of the lattice parameters, thermal expansion coefficients, and elastic constants of ZrB2, TiB2, and HfB2 ceramics at ultrahigh temperatures (up to 2200 K). Equilibrium lattice parameters of the ceramics are determined at finite temperatures. A finite strain method is used to extract the stiffness tensor of the ceramics. The results obtained for ZrB2 and TiB2 agree well with experimental results reported in the literature. Our work demonstrate that accurate properties may be obtained from a statistical averaging of the lattice parameters alone neglecting phonon interactions. [ABSTRACT FROM AUTHOR]

We report on the inhibition of WO3 crystallization by the addition of Ti observed in sputter-deposited W0.95Ti0.05O3 films. The effect of growth-temperature on the crystallization indicates that the W0.95Ti0.05O3 films grown at temperatures <300 °C are amorphous compared to WO3 crystalline films at 100-200 °C. Phase transformation is induced in W0.95Ti0.05O3 resulting in tetragonal structure at ≥300 °C. The corresponding electrical properties exhibit a clear distinction as a function of these structural transformations. Temperature-dependent dc electrical conductivity (80-300 K) shows the semiconducting nature of W0.95Ti0.05O3 films and exhibits two distinct regions indicative of two different types of transport mechanisms. [ABSTRACT FROM AUTHOR]

Nanocrystalline tungsten oxide (WO3) films were grown by reactive magnetron sputter-deposition. The structure and optical properties of WO3 films were evaluated using grazing incidence x-ray diffraction and optical spectroscopic measurements. The effect of ultramicrostructure was significant on the optical characteristics of WO3 films. The band gap decreases from 3.25 to 2.92 eV with increasing grain-size from ∼9 to 50 nm while the films exhibit a transition from monoclinic to tetragonal phase. A direct microstructure-property relationship found suggests that tuning properties of WO3 films for desired applications can be achieved by tuning the conditions and controlling the phase. [ABSTRACT FROM AUTHOR]

Zirconium oxide (ZrO2) thin films with an average crystallite-size (L) ranging from 5 to 25 nm were grown by sputter deposition onto optical grade quartz substrates. The optical properties of grown ZrO2 films were evaluated using optical transmission and reflectance spectroscopic measurements. The size-effects were significant on the optical characteristics of ZrO2 films. The bandgap energy (Eg) was found to increase from 5.78 to 6.07 eV with decreasing L values from 20 to 7 nm. A direct, linear inverse L-Eg relationship found for ZrO2 films suggest that tuning optical properties for desired applications can be achieved by controlling the size. [ABSTRACT FROM AUTHOR]

The optical properties, interface structure, and thermal stability of the ZrO2 films grown on Si(100) were investigated in detail. A 2 nm thick interfacial layer (IL) is formed at the ZrO2–Si interface for the as-grown ZrO2. The optical constants of ZrO2 films and IL correspond to amorphous-ZrO2 and amorphous-SiO2, respectively. The oxidation and IL growth at 900 °C, as a function of annealing time, exhibit a two-step behavior with a slow and a fast growth-rate zones. The transition from a zone of slow to fast rate is attributed to structurally modified ZrO2 facilitating the faster oxygen transport to the ZrO2/Si interface. [ABSTRACT FROM AUTHOR]

LiNi0.8Co0.15Al0.05O2 thin films were prepared by pulsed-laser deposition at varying growth conditions. It was found that the growth and microstructure of the films is highly dependent on the target composition, deposition temperature, and the reactive atmosphere during laser ablation. The x-ray diffraction and Raman spectroscopic measurements indicated the high-structural quality of the grown LiNi0.8Co0.15Al0.05O2 thin films. A phase diagram mapping the effect of temperature on the microstructure of LiNi0.8Co0.15Al0.05O2 thin films has been proposed. The measurements of charge-discharge profiles of Li microcells using the LiNi0.8Co0.15Al0.05O2 films grown at 450 °C demonstrate their possible applications in microbatteries. A stable capacity of 98 μA h/cm2 μm was obtained in the potential range of 4.2–2.5 V for LiNi0.8Co0.15Al0.05O2 films grown at 450 °C. [ABSTRACT FROM AUTHOR]

The structure, dc magnetization and ac susceptibility characteristics of the rare-earth (R = La,Dy) ionsubstituted cobalt-ferrites (CoO.Fe1.925La0.075O3 and CoO.Fe1.925Dy0.075O3) are evaluated. R-substituted Co-ferrites crystallize in the cubic inverse spinel phase. The irreversible temperature (Tirr) between zero field cooled (ZFC) and field cooled (FC) magnetization for CoO.Fe1.925La0.075O3 and CoO.Fe1.925Dy0.075O3 determined from the temperature variation of magnetization measurements are 283 and 292 K, respectively. The broadening of ZFC magnetization and more than one maximum indicates the coexistence of short-range ferrimagnetic clusters of different size with a long-range ferrimagnetic phase. Magnetization curves indicate no saturation up to 30 kOe suggesting the canted spin structure inside the clusters. The relaxation times of spin clusters calculated using theVogel-Fulcher law for the frequency-dependent ac susceptibility measurements are on the order of ∼10-6 s. [ABSTRACT FROM AUTHOR]

HfO2 films were produced by sputter deposition in the substrate temperature (Ts) range of room temperature (RT)-300 °C and their structural, magnetic, and electrical properties were evaluated. The results indicate that the HfO2 films crystallize in the monoclinic structure and are oriented along the (-111) direction. Magnetization measurements (300-1.8 K) evidence their RT ferromagnetism. The effect of Ts is significant on the magnetic moment (M) and coercivity (Hc). M and Hc values enhanced with increasing Ts due to formation of oxygen vacancies. Increase in the temperature from 150 to 300 K decreases Hc without any transition, indicating that the Curie temperature of HfO2 films is higher than RT. Electrical measurements indicate that the HfO2 films are semiconducting. [ABSTRACT FROM AUTHOR]

Molybdenum oxide (MoO3) films were prepared by magnetron sputtering using an Mo target. The films were sputtered in the reactive atmosphere of an argon-oxygen gas mixture under various substrate temperatures, Ts, and oxygen partial pressures, p(O2). The effects of the growth conditions on the microstructure were examined using reflection high-energy electron diffraction and x-ray photoelectron spectroscopy. The analyses indicate that stoichiometric and polycrystalline MoO3 films were obtained at Ts = 445 °C and p(O2) = 61%. The applicability of the sputtered MoO3 films for lithium microbattery application has been demonstrated. The discharge-charge profiles, the kinetics of lithium intercalation process in the film, and the cycling behavior have been investigated in detail to understand the effect of microstructure on the electrochemical performance. [ABSTRACT FROM AUTHOR]