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Lead-free ferroelectric materials are essential for environment-friendly solid-state cooling technology. In this respect, the electrocaloric effect of lead-free Ba0.8−xSr0.2SmxTiO3 (x = 0.01–0.05) ceramics has been investigated. The Rietveld refinement reveals that all the ceramics exhibit tetragonal symmetry and the tetragonality decreases for x > 0.03, which is the major reason behind the decrease in both isothermal entropy change and adiabatic temperature change. The degree of diffuseness parameter is enhanced by doping of Sm3+, which confirms the formation of polar nanoregion and the enhancement of the electrocaloric effect parameter by adding extra entropy. The relaxor behavior of the prepared samples is also confirmed by estimating the degree of deviation parameter [Formula: see text] from the [Formula: see text] curve. So, the temperature stability of the prepared ceramics is improved in a broad temperature window. The highest isothermal entropy change [Formula: see text], adiabatic temperature change [Formula: see text], and electrocaloric strength [Formula: see text] are found to be 1.230 Jkg−1 K−1, 0.862 K, and 0.028 73 K cm/kV at 316 K, respectively, for Ba0.77Sr0.2Sm0.03TiO3.

Temperature-dependent dynamic ferroelectric hysteresis of semiconductor–relaxor ferroelectric (0–3) type composite {0.30(ZnO)–0.70[(Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBTO)]} has been investigated using polarization–electric field ( P– E) loops, current density–electric field ( J– E) curves, and temperature-dependent dielectric permittivity. It is well known that the polarization reversal mechanism can be explained by the concept of ferroelectric domain switching kinetics, which depends strongly on the temperature. The present work ascribes the role of polar nanoregion induced thermal depolarization field on the temperature-dependent ferroelectric hysteresis loop along with polarization reversal mechanism. The present composite exhibits unique ferroelectric switching behavior above the thermal depolarization temperature (∼100 °C), which is observed in P– E and J– E loops. The depolarization field-induced pinched P– E loops of a BNBTO solid solution above Td (∼100 °C) have been significantly overcome by the incorporation of semiconductor (ZnO) particles, which extensively described the underlying mechanism in the present context. In addition, the temperature-dependent polarization reversal mechanism displays unique two-stage processes [low- T (100 °C)] for the minor loops (∼30 and 40 kV) and saturated loops (∼45 kV) as described by the electric field–temperature phase diagram. The present results may provide a distinct way to Bi0.5Na0.5TiO3-based solid solutions for high-temperature piezoelectric applications.

The enhanced electronic memory performance of glancing angle deposited erbium-doped indium oxide (In2O3:Er) transparent nano-column (NCol) based metal-oxide-semiconductor (MOS) structured memory devices is reported. The fabricated MOS devices are Au/In2O3/p-Si, Au/0.26 at. % In2O3:Er/p-Si, and Au/0.48 at. % In2O3:Er/p-Si. The capacitance–voltage (C–V), conductance–voltage (G–V), C–V hysteresis, endurance, and retention properties from the cyclic current–voltage (I–V) curve of the fabricated devices were investigated in detail. The overall interface state density (Dit) for the devices at the different applied frequency (f) decreases with the increase in Er doping. The observations obtained from C–V, G–V, and Dit–f curves were theoretically explained considering a modified delta depletion model. It was found that Au/0.48 at. % In2O3:Er/p-Si does not go to inversion even at a high applied voltage. The constant capacitive memory window (MW) for Au/In2O3/p-Si is ∼1 V at the depletion region. MW increases from ∼0.6 V (sweep voltage ±6 V) to ∼2.5 V (sweep voltage ±16 V) and ∼1.4 V (sweep voltage ±6 V) to ∼6.8 V (sweep voltage ±16 V), respectively, for Au/0.26 at. % In2O3:Er/p-Si and Au/0.48 at. % In2O3:Er/p-Si. The increased MWs despite reduced Dit is explained in detail by primarily considering increased polarization switching of the In-O-Er material, asymmetric charge injection from the top electrode, and the presence of the oxygen-rich environment. The I–V hysteresis performance of the devices under a reverse bias was also improved with Er doping due to the migration of O2− inside the oxide layer. The whole analysis indicates that the gate-controlled Au/0.48 at. % In2O3:Er/p-Si MOS device is appropriate for capacitive memory applications.

The equation of state (pressure-volume relationship) of a monolithic SiC composite has been determined separately by high pressure ultrasonic and x-ray techniques. The ultrasonic measurements were performed on a cylindrical specimen, 2.2 mm in diameter and 2.2 mm in length, in a large-volume uniaxial split cylinder press to 13.6 GPa. The synchrotron measurements were carried out on the polycrystalline sample loaded in a diamond anvil cell up to a pressure of 27 GPa. The room temperature bulk modulus obtained from the ultrasonic measurements is K0=216.5±1.1 GPa and the pressure derivative is K0′=4.19±0.09. The shear modulus obtained is G0=196.7±0.7 GPa with its pressure derivative G0′=0.95±0.03. Using K0′ obtained from the ultrasonic measurements in the Birch–Murnaghan equation to fit the synchrotron x-ray data, we obtain a bulk modulus of K0=218.4±4.9 GPa for the composite.

Surface Brillouin scattering has been used to determine the elastic properties of thin hard submicron cubic boron nitride (cBN) films grown on silicon by mass selected ion beam deposition. The elastic properties of the films have been determined by fitting experimental data to theoretical dispersion curves. A Green’s function method was used to predict Brillouin scattering spectra of the acoustic excitation at the free surface. Our results demonstrate that the effect of the thin hexagonal boron nitride interlayer located between cBN film and the Si substrate on the velocity of the surface acoustic wave does not exceed 2% for a thin (16 nm) film and is negligible for cBN films thicker than 100 nm. The elastic properties of the cBN films are not softer than those of bulk cBN.

The electrical resistivity of TiB2 has been measured using a DIA‐6 cubic anvil apparatus at pressures up to 8 GPa and temperatures up to 800 K. The ambient‐condition resistivity is determined to be 13.3 (±0.9) μΩ cm. The resistivity decreases with increasing pressure. At pressures above 2 GPa, the pressure dependence of the resistivity is about −0.36 μΩ cm/GPa. On heating, the resistivity increases linearly with temperature. The measurements at simultaneously high pressure (3.2 GPa) and high temperatures yield a temperature dependence of 46 (±5) nΩ cm/K for the resistivity.

The compressional VP wave velocity, refractive index n, and acoustic attenuation coefficient Γ of breakaway glass and liquid have been measured by high‐resolution Brillouin spectroscopy up to 170 °C in platelet and backscattering geometries. A marked break in the compressional wave velocity‐temperature relationship is observed at the glass transition temperature of 52 °C consistent with the glass transition temperature observed in ultrasonic experiments on the same sample. The temperature dependence of the compressional wave velocity determined by Brillouin scattering and ultrasonic interferometry are compared.

The longitudinal and transverse velocities of various Ag‐YBa2Cu3O7−δ composite samples have been measured under high pressure in nitrogen gas (up to 0.4 GPa) using ultrasonic techniques. A systematic relationship between the elastic properties and the composition of these composites is observed. The sound velocities of pure YBa2Cu3O7−δ derived from our experimental data are in good agreement with previous results obtained on single crystalline and oriented polycrystalline samples

This study is aimed at establishing a method of polarized/confocal Raman spectroscopy capable of quantitatively assessing crystallographic orientation in wurtzitic GaN with a micron-scale resolution. First, Raman selection rules are explicitly put forward from a theoretical viewpoint in their complete form; then, experimentally retrieved intensities of the Raman signal as a function of Euler angles are fitted to the obtained theoretical dependencies in order to quantify a set of Raman tensor elements using experiments on known crystallographic planes of a wurtzitic GaN single-crystal. According to the above two procedures, a spectroscopic algorithm, incorporating the use of Raman tensor elements and Euler angles in tandem, becomes available for estimating unknown crystallographic orientations. As an application of the developed method, a confocal Raman probe was used to non-destructively unfold the relative orientation of a wurtzitic GaN epilayer with respect to (0001)-oriented sapphire substrate. The mic...

Using Raman spectroscopy, we have studied the optical phonon modes of GaN nucleation layers with the thicknesses of 7 and 45nm, grown on sapphire (0001) substrates by metal organic chemical vapor deposition at low temperatures (500–600°C). These layers consisted of mixed hexagonal and cubic phases. The Raman results from mixed phases were compared with those from pure hexagonal layers which were grown at higher temperatures over 1000°C. The E2H and A1(LO) phonon modes are observed at 548 and 733cm−1 for 45nm thick nucleation layer, while the silent low-frequency B1 mode which is forbidden in good quality hexagonal GaN is observed at 314cm−1. The presence of the strong hexagonal modes for GaN nucleation layers of 45nm thick confirms the crystalline nature of the GaN nucleation layer and dominant hexagonal phase in this mixed cubic-hexagonal nucleation layer. The observed frequencies are shifted with respect to the corresponding A1 and E2 phonon modes in hexagonal GaN. The decrease in mode frequency implies the presence of in-plane tensile strain in these GaN nucleation layers of 45nm thick. The Raman scattering spectra taken from different positions on the sample show similar spectral features, indicating that the GaN nucleation layers of 45nm thick are homogeneous in micron scale.

A direct transformation from the g-BC1.6 phase to a diamondlike BC1.6 phase was obtained in a diamond-anvil cell at high temperature, 2230±140K, and high pressure, 45GPa. Such a transition has not been observed in the B–C system before. The recovered samples were examined using both synchrotron-based x-ray diffraction and confocal micro-Raman spectroscopy at ambient conditions. The lattice parameter of the diamondlike phase (3.5745A) is close to that of diamond. The measured visible laser-excited Raman spectra of a diamondlike BC1.6 phase reveal a peak at 1315cm−1 which is attributed to the LO mode. It is also found that the orthorhombic/hexagonal phase was formed under high pressure in the areas where heating was not enough to make transformation in the cubic phase.

Room temperature investigations of the shear strength of hexagonal TiB2 have been performed in order to determine the hydrostatic equation of state of the material up to 60GPa using radial x-ray diffraction in a diamond anvil cell. We have analyzed the deformation mechanisms under pressure by analyzing the (001) and (100) peaks in the powder diffraction data, and we have deduced the hydrostatic equation of state of TiB2. The uniaxial stresses in the (100), (001), and (101) diffraction planes show a large pressure dependence, indicating a significantly large anisotropy in the material. The stress in the (001) plane shows the largest increase with pressure and reaches a maximum value before the other planes, indicating an initial activation of slip in the (001) plane at the onset of plastic deformation. Compared to gold, the averaged uniaxial stress component in TiB2 is almost 27 times as large at the maximum loading pressure, 60GPa, achieved in the experiment.

The hardness of nanocomposite (nc) films developed recently appears to reach the hardness of diamond. High hardness is commonly attributed to the granular structure of nanocomposites (Hall–Petch effect) [E. O. Hall, Proc. Phys. Soc. Lond. B 64, 747 (1951); N. J. Petch, J. Iron Steel Inst. 174, 25 (1953)]. However, grain size in nanocomposites is generally small (5–15nm) and falls in the region where the Hall–Petch effect does not apply. The objective of the present study is to report the elastic properties of the superhard nanocomposites determined by means of surface Brillouin scattering (SBS), and to compare the results with those obtained by nanoindentation. Two types of nanocomposite films were studied: nc-TiN∕a-Si3N4 and nc-TiN∕a-BN. The SBS measurements presented yield values of Young’s modulus significantly larger than those obtained from the slope of unloading indentation curve. This discrepancy is attributed to the lack of the validity of the assumptions behind the Sneddon’s derivation of the formula used for the calculation of the Young’s modulus from the indentation data.

Pressure‐volume relationships for the bcc transition metals in the groups VB (V, Nb, and Ta) and VIB (Cr, Mo, and W) were determined under hydrostatic pressure to 100 kbar at room temperature by means of x‐ray diffraction, employing diamond‐anvil pressure cell and the ruby (R1 line) fluorescence calibration technique. Using the measured ultrasonic K′0 values, where K0 is the bulk modulus at ambient pressure, for five metals and the deduced shock‐wave K′0 value for Cr, the values of K0 for V, Nb, Ta, Mo, W, and Cr are calculated to be 1.54, 1.71, 1.94, 2.67, 3.07, and 1.93 Mbar, respectively, by least‐squares fit of the experimental P‐V data to the Birch‐Murnaghan equation. The K0 values thus determined are in good agreement with the ultrasonic and shock‐wave values for V, Nb, Ta, Mo, and W. For Cr, the K0 value (1.93 Mbar) is in agreement with the shock‐wave value (1.92 Mbar) but not with the ultrasonic value (1.65 Mbar). This discrepancy can be explained in view of the paramagnetic→antiferromagnetic transition in Cr in the temperature proximity of the ultrasonic measurements (Neel temperature TN∼311 °K at 1 bar) and by the negative pressure dependence of TN.

Structural transformations in pure Zr and Hf and their alloys with 5.2, 21.1, 42.9, and 71.3 at . % Hf have been investigated up to 42 GPa (1 GPa = 10 kbar) at room temperature (∼22 °C) by in situ high‐pressure x‐ray diffraction techniques, using a diamond‐anvil pressure cell. The pressure of transformation a→w increases rapidly with increasing Hf content. On extrapolation, the pressure of transformation a→w for Hf is estimated to be in the order of 60 GPa. Values of the c0/a0 ratio of the pressure‐induced w phase for Zr and its alloys are 0.621±0.002, in good agreement with those of heat‐treated w phases in the Zr‐Nb system.

Infrared absorption spectra of five lithium silicate and six potassium silicate glasses of varying composition (20–35 mole% Li2O and 15–40 mole% K2O, respectively) are examined in the range 1500–100 cm−1. The frequencies of the main absorption bands decrease with an increase of alkali‐metal oxide (M2O) content, with the exception of the −960 cm−1 shoulder for the lithium silicate glasses. The pressure dependences to [inverted lazy s]40 kbar, of all the main infrared absorption frequencies, which are pressure sensitive, are found to be positive. The values of d νi/d P are higher for potassium silicate glasses than for sodium and lithium silicate glasses. The effects of pressure are found to be opposite to the compositional effects. The Gruneisen mode γ's, γi, evaluated from the pressure dependence of the infrared absorption frequencies, are apparently related to the polarizing power of the alkali‐metal ion. The results discussed in light of previous high‐pressure infrared absorption studies of fused silica...

Energy‐dispersive x‐ray diffraction measurements on a mixture of powdered NaCl and Au were carried out at high temperatures up to 600 °C (at atmospheric pressure) and also at simultaneously high temperatures and high pressures (to 425 °C and 10.2 GPa). A modified diamond‐anvil high pressure cell with a mini resistance‐wire heater was used in conjunction with the synchrotron radiation at the Stanford Synchrotron Radiation Laboratory. The temperature of the sample was measured directly by a precalibrated Pt‐Pt 10% Rh thermocouple adjacent to the sample. The pressure of the sample was determined by measuring the molar volume changes in NaCl and deriving the pressure through an equation of state. The measured thermal expansion from 25 °C up to 600 °C for NaCl and Au at 1 atm can be expressed by second‐order polynomials: V/V0(NaCl)=1+(1.08±0.05)×10−4 (T−25)+(7.5±1.1)×10−8 (T−25)2 and V/V0(Au) =1+(4.26±0.85)×10−5 (T−25)+(5.0±20)×10−9 (T−25)2, where T is in °C. These results are in excellent agreement with previ...

The adiabatic elastic moduli of single‐crystal Zr vary linearly with hydrostatic pressures up to 4.7 kbar. The pressure derivatives are dC11/dP=3.93, dC33/dP=5.49, dC44/dP=−0.22, dC66/dP=0.26, dC12/dP=3.42, and dC13/dP=4.25. The average high‐temperature Gruneisen mode γH calculated from this data is in wide disagreement with that calculated from the volume thermal expansion coefficient. It is proposed that this disagreement arises because the negative dC44/dP is caused by the change with pressure in the c/a ratio, rather than the volume change.

Infrared absorption spectra of 12 sodium silicate glasses of varying composition (10 to 45 mole% Na2O) are examined at varying pressures to 58.8 kbar. The pressure dependences of all the infrared absorption frequencies studied are found to be positive. Gruneisen γ's are evaluated from the pressure dependence of the infrared vibrations and elastic parameters. The results are compared with those obtained from previous high‐pressure studies of α‐quartz and several other silicate glasses.

Gerlich has shown that Sheard's model for calculating mode γ's from hydrostatic pressure derivatives of the elastic moduli of hcp Mg and Cd yields Gruneisen γ's at both high and low temperatures that are in good agreement with the γ's derived from thermal‐expansion measurements. For hcp Ti and Zr, however, large differences arise, primarily from very small values for dC44/dP. It is proposed that these small values are caused by the changes in c/a ratio with hydrostatic pressure because of a large dependence of C44 on the c/a ratio. The disagreement with thermal‐expansion data can be removed by taking into account the difference in d(c/a)/dV between hydrostatic‐pressure and thermal‐expansion conditions. The effect of Δ(c/a) is not found in tetragonal TiO2, rutile, where γH is in excellent agreement with the thermal expansion γ∞.

The elastic moduli of single crystals of Mo‐16%Re, Mo‐29% Re, and W‐11% Re have been measured to 0.5 GPa (5 kbar) hydrostatic pressure at room temperature. The composition dependence of the pressure derivatives of the moduli follows the trends established for Nb‐Mo and Ta‐W alloys. This finding was unexpected since the shear modulus, C′ = (C11−C12)/2 has a sharp peak in its composition dependence at e/a = 6.0. The results are explained in terms of the differing effects of compression on different d‐electron subbands. Because dC′/dP decreases with increasing Re content, it is also suggested that the compositional range for stability of the bcc structure decreases with increasing pressure.