Coherent Brillouin Spectroscopy in Solid Parahydrogen

We applied coherent Brillouin spectroscopy to solid parahydrogen, and measured the Brillouin spectra of longitudinal acoustic modes at 5.6K. It was found that the linewidth of these spectra is 1.5MHz. From the observed Brillouin shift and the crystal orientation, the elastic stiffness was determined as C ₁₁=0.355±0.016GPa and C ₃₃=0.432±0.022GPa.     

Temperature effects on the properties of Ge thin films

The effects of substrate temperature (T_s) on the properties of vacuum evaporated p-type Ge thin films have been investigated for 25s<400°C. Increase in the substrate temperature improves the crystallinity and increases the grain size resulting a gradual change from amorphous to polycrystalline structure which was attained above a substrate temperature of 225°C. Low resistive (1×10^–2 ohm-cm) and high mobility (280 cm²/V·s) films were obtained at T_s=400°C. It has been observed that the conduction mechanism in polycrystalline films was dominated successively by hopping, tunneling and thermionic emission as the sample temperature was increased from 40 to 400 K. In amorphous samples, conduction was described in terms of different hopping mechanisms.     

Barium–Strontium and Nickel–Cobalt Solid-State Interdiffusion between Hexagonal W-Ferrites BaM2Fe16O27and SrM2Fe16O27 (M = Ni2+, Co2+)

The Ni, Co, Ba, and Sr profiles in the diffusion zones produced between hexagonal W-ferrites (BaCo₂Fe₁₆O₂₇/BaNi₂Fe₁₆O₂₇, SrCo₂Fe₁₆O₂₇/SrNi₂Fe₁₆O₂₇, SrCo₂Fe₁₆O₂₇/BaCo₂Fe₁₆O₂₇, and SrCo₂Fe₁₆O₂₇/BaNi₂Fe₁₆O₂₇) by annealing at 1520 K were used to evaluate the interdiffusion coefficients of the cations involved by the Boltzmann–Matano method over the whole composition range.     

Structural Changes in the Surface Layers of PdHx Alloys Caused by the Hydride Phase Decomposition

By the method of optical microscopy, we perform the in-situ investigation of the plane polished surfaces of PdH _x alloys (with video recording of the processes of transformation) in the case of their rapid cooling at a rate of 11–20°C·sec^–1 from T _c = 292°C ( = 1.97MPa) with simultaneous lowering of the pressure of hydrogen within the temperature range 100–160°C. In the course of decomposition of the PdH_0.24 alloy according to a scheme ₀ + , the formation of nuclei of the - and -phases and their growth were not detected. However, we observe a simultaneous coherent transformation of the entire surface accompanied by the formation of a surface topography similar to the modulated structures formed as a result of the spinodal decomposition. We discuss the possibility of realization of spinodal decomposition under the described experimental conditions.     

Synthesis, crystal structure and X-ray powder diffraction data of the phosphor matrix 4SrO·7Al2O3

The white phosphor matrix 4SrO·7Al₂O₃ has been synthesized by firing the appropriate mixture of SrCO₃, Al(OH)₃ and H₃BO₃ in the molar ratios 1:3.5:0.135 at 1300°C for 4–7 h. The crystal structure of 4SrO·7Al₂O₃ has been determined as a orthorhombic Pmma space group with a=24.7451(2)Å, b=8.4735(6)Å, c=4.8808(1)Å, V=1023.41(3)ų, Z=2, and D=3.66 g cm^–3 by the Rietveld analysis. The refinement figures of merit are R_p=8.26, R_wp=11.60, R_bragg=4.44 and s=2.61 for 844 reflections with 2<119.94°. And the corresponding X-ray powder diffraction data are presented for search/match analysis.     

Internally Consistent Thermodynamic Description of Three-Component Liquid-Metal Systems at High Temperatures in the Entire Region of Concentration Triangle

A method is suggested for the investigation of the thermodynamic properties of ternary liquid-metal alloys at high temperatures in the entire region of concentration triangle. The method is demonstrated for a Na–K–Cs ternary system. Data are obtained for the enthalpy and Gibbs energy of formation of alloy in the temperature range of 200 T 1200 K and concentration range of 0 x _{i (j, k)} 1. The results reveal a very fine effect associated with the temperature rise, namely, the inversion of excess partial Gibbs energy G¯ _i ^*= RTln _i ( _i is the activity coefficient of the liquid component) and the change of sign of deviation of partial pressure, as well as of total pressure, from the respective values in accordance with Raoult's law. The obtained results may be used to interpret the available literature data on independent measurements of the saturation pressure.     

Interlaminar Fracture Toughness of CF/PEI and GF/PEI Composites at Elevated Temperatures

An experimental study has been conducted to assess temperature effects on mode-I and mode-II interlaminar fracture toughness of carbon fibre/polyetherimide (CF/PEI) and glass fibre/polyetherimide (GF/PEI) thermoplastic composites. Mode-I double cantilever beam (DCB) and mode-II end notched flexure (ENF) tests were carried out in a temperature range from 25 to 130°C. For both composite systems, the initiation toughness, G _IC,ini and G _IIC,ini, of mode-I and mode-II interlaminar fracture decreased with an increase in temperature, while the propagation toughness, G _IC,prop and G _IIC,prop, displayed a reverse trend. Three main mechanisms were identified to contribute to the interlaminar fracture toughness, namely matrix deformation, fibre/matrix interfacial failure and fibre bridging during the delamination process. At delamination initiation, the weakened fibre/matrix interface at elevated temperatures plays an overriding role with the delamination growth initiating at the fibre/matrix interface, rather than from a blunt crack tip introduced by the insert film, leading to low values of G _IC,ini and G _IIC,ini. On the other hand, during delamination propagation, enhanced matrix deformation at elevated temperatures and fibre bridging promoted by weakened fibre/matrix interface result in greater G _IC,prop values. Meanwhile enhanced matrix toughness and ductility at elevated temperatures also increase the stability of mode-II crack growth.     

Fractal Surfaces of ZrO2 , WO3 , and CeO2 Powders

The surface fractal properties of ZrO₂, WO₃, and CeO₂ powders prepared by the thermal decomposition of ZrO(NO₃)₂, (NH₄)₄W₅O₁₇, and (NH₄)₂Ce(NO₃)₆, respectively, were studied by mercury porosimetry. The results demonstrate that these oxides may, in principle, have fractal surfaces owing to topochemical processes of the type A(s) B(s) + C(g). The surface fractal dimension of individual crystallites and their aggregates are determined.     

Application of Raman in phase equilibrium studies: the structures of substitutional solid solutions of KNO3 by RbNO3

Raman spectroscopy was employed to investigate the KNO₃-RbNO₃ system. Raman studies indicated that Rb⁺ may substitute K⁺ up to 67 mol% in the solid solutions of the KNO₃ II structure (denoted as K_1–x Rb_xNO₃ (KII)) and up to 80 mol% in the solid solutions of the KNO₃ III structure (denoted as K_1+x Rb_xNO₃ (KIII)). The substitutional crystals retained the transitions of I to III to II of KNO₃ on cooling and the metastable property of KNO₃ III at room temperature. It was found that rubidium nitrate had a considerable tendency to have the structure of potassium nitrate. This accounts for the fact that larger rubidium ions can replace many more smaller potassium ions in the nitrate than vice versa. When the concentration of rubidium ions was more than 67 mol%, the substituted crystals underwent the mixed structural phase transition of the KNO₃ III structure to the RbNO₃ IV structure, and K_1–x Rb_xNO₃ (KIII) seemed to consist of disordered R3m microstructure.     

Densities of Sulfur Hexafluoride and Dinitrogen Monoxide over a Wide Temperature and Pressure Range in the Sub- and Supercritical States

Densities of sulfur hexafluoride (SF₆) and dinitrogen monoxide (N₂O) have been measured with a fully computer-controlled high-temperature high-pressure vibrating tube densimeter system in the sub- and supercritical states. The uncertainty in density measurement was estimated to be between ±0.2 and ±0.3kg·m^–3 depending on the temperature. With respect to accuracy, reliability, suitability, and time consumption, this system has significant advantages for measuring PT properties in the compressed liquid and supercritical states. The densities were measured for temperatures from 273 to 623K and at pressures up to 30MPa for SF₆ (442 data points) and from 273 to 473K and up to 40MPa for N₂O (251 data points), which encompassed density ranges between 142.9 and 1778.5kg·m^–3 for SF₆ and between 124.4 and 1051.1kg·m^–3 for N₂O. Furthermore, the liquid densities of SF₆ and N₂O were correlated with a new three-dimensional density correlation system (TRIDEN) and the complete set of PT data in the sub- and supercritical states were correlated with a virial-type equation of state. For checking the accuracy and suitability of the vibrating tube densimeter system, the experimental densities of SF₆ were compared with published data and with the results of a reference equation of state.     

Preparation of LiTaO3 , LiNbO3 , and NaNbO3 from Peroxide Solutions

A procedure is described for preparing peroxide solutions of LiTaO₃ and LiNbO₃. It is shown that the use of peroxide solutions makes it possible to obtain stoichiometric LiTaO₃, LiNbO₃, and NaNbO₃ and Li _x Na_{1 – x} Nb₃ solid solutions.     

The piezoresistance coefficients of copper and copper-nickel alloys

This paper attempts to further a better understanding of the piezoresistance coefficients by studying the piezoresistive effects in copper and copper-nickel alloys. The experimental evidence of isotropic piezoresistance coefficients (₁₁=₁₂) has been obtained for the annealed copper and copper-nickel alloys. The piezoresistance coefficients of the cold-worked copper and Cu₆₀Ni₄₀ alloy are of the tensor character (₁₁₁₂). A physical explanation has been given to the change of the ( _ij ) tensor.     

X-ray-Induced Paramagnetic Centers in SiO2Xerogels

SiO₂xerogels prepared by a sol–gel process followed by sintering at 350–1100°C were irradiated with 30-keV x-rays at a dose rate of 80 R/s. The room-temperature electron spin resonance (ESR) spectra of the xerogels showed signals arising from radiation-induced intrinsic defects (E" centers and terminal oxygens) and organic radicals. By recording ESR spectra in a vacuum of 10^–2Pa, surface E" centers differing in relaxation time from the volume centers were identified for the first time. The ESR signal from the E" centers was measured as a function of x-ray dose. The possible mechanisms for the formation of E" centers under x-ray irradiation are discussed.     

Influence of pore volume on laser performance of Nd : YAG ceramics

For present study, 1.1 at% Nd-doped YAG ceramics with a controlled pore volume (150–930 vol ppm) were fabricated by a solid-state reaction method using high-purity powders. The scattering coefficients of Nd:YAG ceramics, obtained from Fresnel' equation, increased simply with increases in the pore volume. The cw laser output power of Nd:YAG ceramics was clearly related to the scattering coefficients of the specimens examined in the present works, which in turn were affected on the pore volume. The effective scattering coefficients of Nd:YAG ceramics with a pore volume of 150 vol ppm were nearly equivalent to those of a 0.9 at%Nd:YAG single crystal by Czochralski method. As the exciting power was increased under excitation by an 808-nm diode laser, however, the laser output power of the Nd:YAG ceramics exceeded that of the Nd:YAG single crystal because of the fairly large amount of Nd additives. The lasing performance of the Nd:YAG ceramics changed drastically with change in pore volume. On the other hand, lasing performance was not affected by the existence of grain boundaries in the polycrystalline Nd:YAG ceramics.     

The AC electrical characterization of the solid-state reaction derived CaSnO3

The potential of CaSnO₃ (calcium metastannate) for its application as a capacitor component possessing small temperature coefficient of capacitance (TCC) in electrical systems, is examined via the ac small-signal measurements. The ac electrical data were acquired on these samples sintered at various combinations of temperature-time frames (1200°CT1350°C; 24 ht60 h) in the frequency range from 5 Hz to 13 MHz. The measurements were carried out over the temperature range 25–300°C. The electrical response was found to exhibit relaxation processes in more than one complex plane formalism in a simultaneous fashion. The resistance of the sintered samples was dominated by the grain boundaries. The capacitance showed almost linear behavior in this measurement temperature range. The resulting electrical behavior has been discussed with the evolved microstructure in the sintered bodies.     

Na0.25Cu0.75VO3: A New Perovskite-like Vanadium Bronze

A new cubic perovskite-like vanadium bronze of composition Na_0.25Cu_0.75VO₃, with a lattice parameter of 7.2517(1) Å, is obtained by reacting NaVO₃, V₂O₅, and Cu₂O at 1100°C and 8 GPa. It exhibits metallic conduction, with a sharp change in resistivity above 200°C, and, presumably, undergoes a phase transition near 280°C. The thermal properties of the new vanadium bronze are studied in air and helium at normal pressure.     

Liquid phase sintering of RE2O3: YSZ ceramics Part I Grain growth and expelling of the grain boundary glass phase

Experiments on silicate liquid phase sintering of YSZ ceramics with addition of 0.5 mol% of rare earth ions have been done in order to study the effect of these ions on the kinetics of grain growth and the expulsion of glass through the grain boundaries. Kinetics follow a third power law in the following order YPr>YPrEr>YY>YEr. The expelled glass does not spread over the ceramic grains and its mass is inversely related to grain size. Glass phase separation inside the grain boundaries is found to be a necessary condition for glass expulsion.     

Thermodynamic Modeling of BC x N y Chemical Vapor Deposition in the B–C–N–H System

Thermodynamic analysis of the chemical vapor deposition of BN-based films in the B–C–N–H system was carried out for reduced pressures (133 and 1.33 Pa) and a wide temperature range (300–1300 K). The results indicate that, using mixtures of trimethylamineborane, (CH₃)₃N · BH₃, with H₂, NH₃, or N₂, one can produce films of various compositions: from BN to mixtures of BN, carbon, and boron carbide.     

Preparation of Thick LaCu1 – x Ni x O2.5 + δ Films Exhibiting a High-Temperature Metal–Semiconductor Transition

The conditions for producing thick LaCu_{1 – x} Ni _x O_{2.5 +} films on different substrates were optimized. The effects of the heat-treatment conditions, substrate material, and the nature of the liquid organic binder on the composition, structure, and properties of the films were studied. Single-phase coatings obtained on MgO, ZrO₂, BaSO₄, and Ni substrates 50 to 200 m in thickness were close in properties to bulk LaCu_{1 – x} Ni _x O_{2.5 +} and exhibited a metal–semiconductor transition at about 500°C.     

Ferroelectric Lead Zirconate Titanate Films Prepared by Spray Pyrolysis of Carboxylate Solutions

Ferroelectric PbTi_0.6Zr_0.4O₃films 0.5–1.5 m in thickness were produced on platinum substrates by spray pyrolysis of carboxylate solutions. The optimized compositions of the precursor solutions, containing methacrylic acid and ethylene glycol, are stable under normal conditions, allow the annealing temperature to be reduced, and lead to higher quality film surfaces and large grains. The film exhibit the following electrical properties: T _C= 360–460°C, _max= 1750 at T _C, tan = 0.02–0.1 at 1 kHz and room temperature, P _{s max} = 18 C/cm², P _{r max} = 15 C/cm²at 50 Hz, and E _c= 42–120 kV/cm.