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.     

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.     

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.     

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.     

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.     

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.     

Investigation of the Electrophysical Characteristics of SF6Gas: Obtained Results

The radiation-induced electrical conductivity of SF₆gas is experimentally investigated at different pressures. The dependences of the coefficient of attachment of electrons to SF₆molecules on the E/Nratio are determined. The obtained results are compared with the results of numerical calculation by the Monte Carlo method and with the data of other authors.     

The separation of the fracture energy in metallic materials

The total plastic strain energy which is consumed during fracture of a plain-sided CT specimen is separated into several components. These are the energies required for deforming the specimen until the point of fracture initiation, for forming the flat-fracture surfaces, for forming the shear-lip fracture surfaces, and for the lateral contraction and the blunting at the side-surfaces, W _lat. Characteristic crack growth resistance terms, R _flat and R _slant, are determined describing the energies dissipated in a unit area of flat-fracture and slant-fracture surface, respectively. R _flat is further subdivided into the term R _surf, to form the micro-ductile fracture surface, and into the subsurface term, R _sub, which produces the global crack opening angle. Two different approaches are used to determine the fracture energy components. The first approach is a single-specimen technique for recording the total crack growth resistance (also called energy dissipation rate). Plain-sided and side-grooved specimens are tested. The second approach rests on the fact that the local plastic deformation energy can be evaluated from the shape of the fracture surfaces. A digital image analysis system is used to generate height models from stereophotograms of corresponding fracture surface regions on the two specimen halves. Two materials are investigated: a solution annealed maraging steel V720 and a nitrogen alloyed ferritic-austenitic duplex steel A905. For the steel V720 the following values are measured: J _i=65kJ/m², R _surf=20kJ/m², R _flat=280kJ/m², R _slant=1000kJ/m², W _lat=30J. For the steel A905 which has no shear lips, the measured values are: J _i=190kJ/m², R _flat=1000kJ/m², and W _lat=45J. Apart from materials characterization, these values could be useful for predicting the influence of specimen geometry and size on the crack growth resistance curves. Key words: Elastic-plastic fracture mechanics, fracture energy, energy dissipation rate, fracture surface analysis.     

Cast and aged β-NiAl-β′-Ni2AlTi-γ′-Ni3Al-α-Cr alloys: a microstructural and mechanical properties investigation

Microstructural development and stability in cast Ni-30 at% Al-21 at% Cr-4 at% Ti, Ni-28 at% Al-18 at% Cr-6 at% Ti and Ni-26 at% Al-19 at% Cr-8 at% Ti alloys are examined in this paper. The paper considers the extent to which microstructural control and stability is improved in these alloys, when compared with earlier work by the authors on similar materials with lower aluminum (25 or 26 at%) and higher titanium (11 to 15 at%) contents. The paper discusses detailed transmission electron microscopy investigations of both as-cast and aged (140 h at 850 and 1100°C) samples. Attention is focussed on the transformation of L2₁ type (nominally Ni₂AlTi) dendrites. In particular, the influence of the formation of intradendritic L1₂ type (nominally Ni₃(Al,Ti)) on the stability of the -phase is examined. Morphological changes and phase transformations within a --Cr eutectic are discussed. Various modes of second-phase precipitation are considered. The microstructures of selected samples are correlated with mechanical properties determined by tensile testing and fractography.     

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 and dielectric properties of pyrochlore solid solutions in the Bi2O3-ZnO-Nb2O5-TiO2 system

Phase studies of solid solutions based on (Bi_1.5Zn_0.5)(Ti_1.5Nb_0.5)O₇ revealed extended regions of pyrochlore formation in the Bi₂O₃-ZnO-TiO₂-Nb₂O₅ system. At room temperature and 1 MHz (Bi_1.5Zn_0.5)(Ti_1.5Nb_0.5)O₇ has a high permittivity ( = 200), low dielectric loss (tan<1·10^–4) and a temperature coefficient of the permittivity, , = –1300ppm/K. Pyrochlore solid solutions based on (Bi_1.5Zn_0.5)(Ti_1.5Nb_0.5)O₇ can be formed with (Bi_2–xZn_x)(Ti_{2– x} Nb_x)O₇ (0.35x1.0) and with (Bi_1.5 Zn_0.5–y/3Ti_1.5+yNb_0.5–2y/3) O₇ (–1.5y0.75). Investigations of the dielectric characteristics showed that the high temperature dependence of the permittivity of (Bi_1.5 Zn_0.5)(Ti_1.5Nb_0.5)O₇ can be significantly modified by changing the composition of the pyrochlore within these regions of solid solubility. Below room temperature several of these compositions also exhibit a diffuse frequency dependent maximum in their permittivity characteristic of a transition to a relaxor type ferroelectric state. A third region of high permittivity pyrochlores with (Bi_1.5+2zZn_0.25–z Ti_2.25–z)O₇ (0.0z<0.15) was also identified in the Bi₂O₃-ZnO-TiO₂ sub system.     

Preparation and Magnetic Properties of CuCr1 – x Mn x S2 Solid Solutions

Phase relations in the CuS–CrS–MnS system (20 mol % MnS) were studied. The system was found to contain CuCr_{1 – x} Mn _x S₂ solid solutions isostructural with CuCrS₂. The solid-solution range and the oxidation states of Cr and Mn were determined.     

Viscosity of the Grain-Boundary Phase and Sintering of TiB2-Modified Alumina

A model is proposed for the sintering of powders via the sliding of particles facilitated by a grain-boundary phase. Data on the initial-stage sintering kinetics of TiB₂-modified alumina are used to assess the temperature-dependent viscosity of the grain-boundary phase, formed by Al₂O₃, oxidation products of TiB₂, and impurities present on the surface of alumina particles. In the range 1570–1620 K, the temperature variation of viscosity is fitted well by the expression 25.9exp(143308/RT).     

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.     

Thermodynamic Properties of HFC-227ea

The density and speed of sound in gaseous and liquid 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) have been studied by a -attenuation technique, an ultrasonic interferometer, and an isochoric piezometer method over the temperature range of 273 to 383K at pressures up to 3.5MPa. The purity of the samples used throughout the measurements are 99.99mol%. The pressures of the saturated vapor were measured over the same temperature range. The experimental uncertainties of the temperature, pressure, density, and speed of sound measurements were estimated to be within ±20mK, ±1.5kPa, ±0.2%, and ±(0.15–0.2)%, respectively. On the basis of the obtained data, the isobaric molar heat capacity of HFC-227ea was calculated for the ideal-gas state.     

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.     

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.     

Piezoelectric and dielectric properties of PZN-BT-PZT solid solutions

Pb(Zn_1/3Nb_2/3)O₃ ceramics with the perovskite structure can be stabilized by substituting 6–7 mol % BaTiO₃ (BT). Piezoelectric and dielectric properties of the pseudo-binary system (1–x)(0.94PZN-0.06BT) -xPb(Zr_(1–y)Ti_y)O₃ were studied, and the effects of Zr/Ti ratios and thermal annealing process on the piezoelectric and dielectric properties were also discussed. The results show that the piezoelectric properties of this ceramic system are very good when x is about 0.50 and y is about 0.47 with K_p = 70%, d₃₃=560 pC/N, _m #x2248;23,000. These ceramics are favorable to piezoelectric actuators.     

New Types of Resistance Strain Gauges Made of Semiconductor Whiskers

We created resistance strain gauges on the basis of threadlike semiconductor monocrystals of tellurium and selenium and investigated their deformation characteristics under uniaxial tension and compression (up to ± 2.6·10^–3) and hydrostatic pressure (up to 5·10⁸ Pa). Their characteristics are compared with the parameters of resistance strain gauges made of p-type silicon. We developed electric contacts for selenium crystals and concluded that resistance strain gauges are promising for investigation of composite materials under triaxial compression.     

Optical Properties of Ca3Ga2Ge4O14 Crystals

The optical absorption, induced-absorption, luminescence, and excitation spectra and temperature-dependent luminescence intensity of thermochemically colored Ca₃Ga₂Ge₄O₁₄ crystals were measured. The results indicate that the induced-absorption bands at 34000–28000 and 28000–20000 cm^–1 and the emission band at 14800 cm^–1 are related to F-centers.