Structural transformations at semiconductor-metal transition

In the ranges of semiconductors - binary compounds M_nX_m, where M - metal, X - element of IY, Y, YI group of the Mendeleev periodic system, n,m=1,2,3, the semiconductor-metal transition is followed by the structural transformation. As a rule, in the isostructural ranges the semiconductor-metal transitions are not observed. Vectors connecting the overlapping band structure gaps show the direction of structure distortion.     

Thermophysical properties of liquids at high pressures

Most of the thermophysical properties of fluids are greatly altered at high pressures, and the studies of these changes are of much scientific and technological importance. In this paper, the effects of temperature and pressure on the density, viscosity, and thermal conductivity of various liquids are described briefly, based on recent experimental results from the author's laboratory. The objectives of this investigation, methods of measurements, and some of the experimental results are reviewed, as well as the present aspects in this field. Several important problems to be interpreted are also pointed out from the present measurements.Presented at the Japan-United States Joint Seminar on Thermophysical Properties, October 24–26, 1983, Tokyo, Japan.     

Optical properties of semiconductor-metal composite thin films in the infrared region

Germanium:silver (Ge:Ag) composite thin films having different concentrations of Ag, ranging from 7% to 40%, have been prepared by dc cosputtering of Ge and Ag. The films' surface morphology and optical properties have been characterized using transmission electron microscopy and infrared spectrophotometry. It is seen that, although the films that contain lower concentrations of Ag have islandlike morphology (i.e., Ag particles distributed in a Ge matrix), the higher metallic concentration films tend to have a symmetric distribution of Ag and Ge. The optical constants (i.e., refractive index n and absorption index k) derived from the measured optical properties show a semiconductor behavior even as high as 40% of Ag concentration, beyond which the metallic properties dominate over the entire infrared spectrum. Comparison of the n and k data with the two well-known effective medium theories, namely, the Maxwell-Garnett theory and the Bruggeman theory, shows that both theories have limited scope in predicting the optical properties of semiconductor-metal composite films in the infrared region. However, an empirical polynomial equation can simulate the experimental data at all wave numbers of the IR spectrum.     

Thermodynamic properties of a fluid at high pressures

We present formulas for the thermal coefficients of a fluid at high pressures. The formulas are obtained on the basis of the Tate equation of state. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 2, pp. 236–238, March–April, 1997.     

Ground-state properties of solid H2 at high pressures

A simple variational calculation, based on a Heitler-London wave function, is used to describe the high-pressure properties of solid hydrogen at O K. The system properties are expressed as a power series in , which is utilized to investigate the onset of classical behavior. The high-pressure results for the energy and the pressure-volume relation are in close agreement with a recent calculation which used the Domb-Salter approximation. Information is given on the pressure dependence of the two-body correlations in the solid.     

Effect of simple stress on the glass transition of polymers at high pressures

Experimental studies, which have been carried out in this laboratory, showed the yield strength in tension, compression, and shear in the rubbery and the glassy states increased with increasing hydrostatic pressure. Moreover, the Young's modulus also increased with pressure and the amount of the increase across the glass transition temperature (T _g) at a given pressure can be as large as three orders of magnitude in the case of elastomers. An extension of the Gibbs-Dimarzio theory is proposed to account for the effect of applied stress on the glass transition temeprature of glass-forming polymers. When a simple stress, such as tensile, compressive or shear stress, is applied to a polymer, the T _g will decrease, compared to a polymer without applied stress. A glass-forming polymer in the vicinity of the transition would behave differently from that predicted by rubber elasticity. The partition function taking into account the effect of stress is suggested to be $$\Gamma = \Sigma W(f, n_0 ){\text{ }}\exp {\text{ }}[ - \beta (PV + U - \sigma V\varepsilon )]$$ where the strain ?=σ (f ? f ₀) in which f and f ₀ are the fraction of flexed bonds with and without stress, respectively. Furthermore, by this model, the Young's modulus across the transition, E _L and E _G, can be evaluated. The Young's modulus increases with increasing pressure at lower and moderate pressure range but the increase is rather small at very high pressure range.     

Thermoelectric elements based on compounds of silicon and transition metals

Semiconducting compounds based on silicides of 3d transition metals (MnSi_1.75 and CoSi) are promising thermoelectric materials for mass-produced thermoelectric generators. Their practical use has been delayed so far by the lack of reliable switching. Electrochemical surface treatment technology and metal deposition were used to obtain thermal-cycling-resistant, switching and antidiffusion metal coatings (Ni, Co, Fe, Cr) with an electrical resistivity up to 10⁻⁶ Ω·cm² in the metal-semiconductor region. This technology was applied to develop a series of thermoelements and thermoelectric generators having wide-ranging applications. Pis’ma Zh. Tekh. Fiz. 23, 64–69 (August 12, 1997)     

A theoretical and experimental approach to the active-to-passive transition in the oxidation of silicon carbide: Experiments at high temperatures and low total pressures

Active-to-passive oxidation transition in chemical vapour deposited -SiC was investigated in the temperature range 1300T1700°C under low total pressures (100Ptot800 Pa) and relatively high linear gas flow rates (10Vgas60 m s1) by thermogravimetric analysis. For given T, Ptot and Vgas, the oxygen partial pressure at the transition, PtO2, corresponds to the value where the mass-loss rate per unit area of the oxidized sample, R, is maximum. Logarithms of PtO2 are linear functions of reciprocal temperature for given Ptot, and Vgas. Vgas has a significant influence on the position of the transition log(PtO2)–T-1 line. PtO2 is also slightly affected by an increase of Ptot from 100 Pa to 800 Pa. In passive oxidation at high temperatures (>1500°C), large bubbles form in the silica film which is then disrupted leading to a loss of material. In active oxidation, R significantly depends on Vgas: the kinetics is diffusion or mass transfer controlled under the conditions investigated in the present study. In both active and passive oxidation regimes, a mass loss of the test specimen is always observed; an explanation is proposed.     

Volumetric properties of mixtures of fluoroalcohols and water at high pressures

Densities of aqueous solutions of 2,2,2-trifluoroethanol, 2,2,3,3-tetranuoropropanol, and 2,2,3,3,3-pentanuoropropanol have been measured with a vibrating-tube densitometer. Measurements were performed at temperatures of 298 and 323 K and at pressures up to 80 MPa with an estimated uncertainty of ±0.2 %. Molar volumes obtained for these mixtures are correlated with pressure by the Tait equation within the experimental uncertainty. Excess molar volume, isothermal compressibility, and partial molar volume of these mixtures are determined in terms of this correlation equation and compared with those of the aqueous solutions of hydrocarbon alcohols. Composition dependence of partial molar volume is discussed in comparison with that of Raman spectroscopic data.     

Structure and magnetic properties of YCo_5 compound at high pressures

The crystal structure and magnetic properties of YCo_5 compound have been studied by neutron diffraction,in the pressure range 0 ≤ p ≤ 7.2 GPa.The cobalt moments decrease with pressure,parallelly with anisotropic changes of lattice parameters.The experimental data are analyzed together with results from the combined Density Functional and Dynamical Mean-Field Theory.A rather good agreement between the experimentally determined and calculated values of cobalt moments is shown.Our scenario for the behavior of YCo_5 under pressure,is the combined action of the Lifshitz transition with a strong local electron-electron interaction.     

Thermodynamic properties of cesium and potassium at high pressures and temperatures

Results are presented of PVT experiments of cesium and potassium in the gas phase. An equation of state is derived and tables of the thermodynamic properties of cesium vapor are computed. A survey is given of the PVT properties of cesium in the liquid phase.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 6, pp. 986–992, December, 1980.     

Theoretical study of the thermodynamic properties of nitrogen at high temperatures and pressures

A theoretical analytical equation of state is derived and used to compute new thermodynamic data for nitrogen at high tempratures and pressures.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 6, pp. 975–983, December, 1987.     

Measurements of caloric properties of fluids at low temperatures and high pressures

The information about the caloric properties of materials is important for the design of low temperature processes. The design of a multipurpose flow calorimeter is explained. The average heat capacity, the isenthalpy and the isothermal throttling effect of pure nitrogen were determined and compared with other available data.     

Volumetric properties of mixtures of 1,4-dioxane and water at high pressures

Densities of aqueous of 1,4-dioxane have been measured at temperatures from 298 to 348 K and at pressures up to 40 MPa by a vibrating-tube method. Molar volumes obtained with an estimated uncertainty of ±0.2°,% are correlated with pressure by the Tait equation within the experimental uncertainty. Pressure and composition dependences of the excess molar volume, partial molar volume, and isothermal compressibility are determined and they are compared with those of other aqueous solutions.     

Fast neutron bombardment induced semiconductor-metal electron transition in lead selenide

We have studied the electrical and galvanomagnetic properties of p-PbSe single crystals irradiated with fast neutrons. Changes in the temperature dependence of the resistivity and the Hall constant show evidence of the metal-semiconductor electron transition. Subsequent annealing at 350–390 K leads to a partial recovery of the initial properties and the reverse electron transition.     

Experimental investigation of the thermal properties of a binaryn-hexane-water mixture at high temperatures and pressures

The results are presented of an experimental investigation of the thermal properties of a binaryn-C₆H₁₄ + H₂O mixture (system) in the ranges of temperature from 372.75 to 690.55 K, density from 66.87 to 834.30 kg/m, and pressure from 0.4 to 65.7 MPa. Measurements are performed for seven values of water concentrationx (in molar fractions), namely, 0.166, 0.257,0.347,0.615,0.827,0.935, and 0.964. The investigations cover the region of liquid-vapor phase equilibrium and extend further into the homogeneous region. In order to describe theP-V-T-x properties of a binary n-hexane-water mixture, the Soave-Redlich-Kwong formula is used (the average error is 3%, and the maximum error is 8%). Based on the scaling equations, the critical indices and amplitudes for the curves of liquid-vapor coexistence are calculated for three values of water concentration.     

The measurement of humidity at high pressures

A humidity calibrator for measurements at pressures up to 15 MPa is designed. The effect of pressure on the characteristics of capacitive humidity sensors is demonstrated. A method of taking this effect into account is proposed. A procedure for calibrating humidity transducers with capacitive sensors at high pressure is described. __________ Translated from Izmeritel’naya Tekhnika, No. 2, pp. 61–64, February, 2008.