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.     

Influence of the α/β-SiC phase transformation on microstructural development and mechanical properties of liquid phase sintered silicon carbide

The transformation kinetics and microstructural development of liquid phase sintered silicon carbide ceramics (LPS-SiC) are investigated. Complete densification is achieved by pressureless and gas pressure sintering in argon and nitrogen atmospheres with Y2O3 and AlN as sintering additives. Studies of the phase transformation from to -SiC reveals a dependency on the initial -content and the sintering atmosphere. The transformation rate decreases with an increasing -content in the starting powder and in presence of nitrogen. The transformation is completely supressed for pure -SiC starting powders when the additive system consists of 10.34 wt% Y2O3 and 2.95 wt% AlN. Materials without phase transformation showed a homogeneous microstructure with equiaxed grains, whereas microstructures with elongated grains were developed from SiC powders with a high initial /-ratio (>1:9) when phase transformation occurs. Since liquid phase sintered silicon carbide reveals predominantly an intergranular fracture mode, the grain size and shape has a significant influence on the mechanical properties. The toughness of materials with platelet-like grains is about twice as high as for materials with equiaxed grains. Materials exhibiting elongated microstructures show also a higher bending strength after post-HIPing.     

A re-examination of the Kraft and Flinn diffraction data for Cr2B, (Cr,Fe)2B, and the boride phase in Fe + 18.5 wt % Ni + 20 wt % Cr + B alloys

Kraft and Flinn's [2] powder X-ray diffraction data obtained from excess-phase particles in Fe + 18.5 wt% Ni + 20 wt% Cr + B alloys have been analyzed. The major boride phase was determined to be (Cr,Fe)2B (orthorhombic, Fddd, isomorphous with Cr2B). Its lattice parameters, a = 1.4585 ± 0.0010 nm, b = 0.7331 ± 0.0005 nm, c = 0.4223 ± 0.0003 nm, are indicative of the composition (Cr1.04±0.08Fe0.96 ± 0.08)B. It was not possible to identify the phase(s) giving rise to a much weaker set of diffraction lines in the patterns. Of the two alloys used by Kraft and Flinn as standards, the one intended to be Cr2B was found to be a mixture of Cr2B and Cr5B3. The second, intended to be Cr1.0Fe1.0B was determined to be Cr0.67± 0.07Fe1.33± 0.07B.     

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.     

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.     

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.     

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.     

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.     

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.