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Film structures based on Si1–xGex (0 < x < 1) solid solutions are currently obtained by chemical-vapor-deposition methods. For device application of the obtained structures, it is necessary to know the electrical properties of the material synthesized under different conditions. In this work, we carry out galvanomagnetic studies of the electrical conductivity in porous and solid Si1–xGex films, as well as the concentration and mobility of the majority charge carriers in them at a temperature of 30–300 K. It is shown that, as in pure silicon and germanium of comparable porosity, the electrical conductivity in the studied samples can be considered as in a medium with voids. It is established that the type of majority charge carriers in the alloy is determined by the type of silicon substrate used. This is practically important for creating both arms of a thermoelectric converter, which makes the method for producing Si1–xGex(0 < x < 1) alloy promising for device applications, in particular in thermoelectric converters and lithium-ion batteries. [ABSTRACT FROM AUTHOR]

In the present work, Si65-xGe31Au4Bx (x = 1, 2, 3, and 4) nanocomposites were synthesized by ball milling and spark plasma sintering to investigate the boron concentration dependence of thermoelectric properties. The electrical resistivity observed for samples made at 2 ≤ x ≤ 4 was almost constant over a wide temperature from 300 K to 1000 K, indicating the strongest scattering limit with disordering. All samples possessed the large Seebeck coefficient, mainly, B-1% and B-3% doped sample shows the significant Seebeck coefficient exceeding 450 μVK−1, which was presumably attributed to a sharp peak in the electronic density of states near the valence band edge. As a result, the largest power factor of 2.1 mWm−1K−2 was observed at x = 3. In addition, the lowest thermal conductivity less than 1.3 Wm−1K−1 was observed for x = 2,3, and 4. The significant power factor, together with low thermal conductivity naturally led to obtain high ZT value of 1.63 at 973 K. This value is much higher than that of previously reported other Si-Ge based nanocomposites. [ABSTRACT FROM AUTHOR]

Si 0.7 Ge 0.3 was prepared by rapid cooling (∼330 °C/min) to get the fine grain structure for high thermoelectric performance. The same material was prepared under slow cooling (1 °C/min) for comparative analysis. The results were out of our expectation as the EBSD pattern revealed almost same grain structure of both samples. To know the reason for the similar grain structures, crystal growth of Si 0.7 Ge 0.3 sample was in-situ observed under rapid and slow cooling. During rapid cooling, initially grown fine dendrites were completely re-melted and recrystallized on further cooling. No re-melting was occurred in Si under rapid cooling. Due to the growth of Si-rich Si 1-x Ge x dendrites at high temperature the melt becomes Ge richer thereby initially grown fine dendrites were re-melted to reach equilibrium liquidus composition. Moreover, the similar grain structures of Si 1-x Ge x under rapid cooling as well as slow cooling was originated from the re-melting of initially grown fine dendrites and recrystallization at relatively low temperature. • Si 1-x Ge x was prepared under rapid (330 °C/min) and slow cooling (1 °C/min) processes. • EBSD of both samples show same grain structures despite of different cooling rates. • To understand the grain structure formation, Si 1-x Ge x growth was in-situ observed. • Re-melted was observed in Si 1-x Ge x , while Si was not re-melted under rapid cooling. • Same grain structures were attributed due to re-melting and recrystallization. [ABSTRACT FROM AUTHOR]

Abstract The thermophysical properties and atomic structure of liquid Si-Ge alloys were investigated by the molecular dynamic simulations with Stillinger-Weber potential over a broad temperature range, including both superheating and undercooled regime. The maximum undercooling in this work is 611 K for pure Ge. For all the Si 100- x Ge x (x = 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100) alloys, the densities exhibit quadratic relationship with temperature. The density of Si at the melting temperature is 2.59 g·cm−3, existing a slight deviation of 0.39% compared with the experiential data. For liquid Ge, the density at the melting temperature is 5.62 g·cm−3, nearly identical with the reported values. In all the cases, the densities of Si-Ge alloys with different compositions are larger than those of ideal solution. Therefore, liquid Si-Ge alloys display negative excess volume, which reaches the minimum at 40% Ge content. The specific heat was obtained by thermodynamic function and energy fluctuation approaches, respectively. Both of the results are in good agreement with experimental data around the liquidus temperatures. Furthermore, the diffusion coefficients were obtained by calculating the mean square displacement. The pair distribution function was applied to analyze the liquid structure. It is found that the peaks occur around the liquidus temperatures, which implies the structure change between normal and undercooled liquid alloys. Highlights • The temperature range is much broader, including 600–2500 K for Ge. • The difference between calculated and reported density for Si and Ge is less than 4%. • The structure change between normal and undercooled liquid was observed. [ABSTRACT FROM AUTHOR]

n-Type Si-Ge thermoelectric alloys were prepared using a melt spinning (MS) process, and then the microstructures of the samples were investigated. The alloys studied were ribbon shaped with a thickness of about 30 μm. Scanning electron microscopy (SEM) along with energy-dispersive spectrometry (EDS) and x-ray diffraction (XRD) showed a predictable, homogeneous, fine-grained microstructure at the high cooling rate, different from those of samples created by slow solidification (SS). [ABSTRACT FROM AUTHOR]

Silicon and germanium alloys have been formed for the first time by heating powdered mixtures of 75%Si and 25%Ge in just 2 min in the H field in a single mode 245 GHz microwave cavity. As is well known, alloy formation in conventionally heated silicon-germanium mixtures is difficult, even when processed for much longer time durations at the same temperature. Further, any oxide contaminants, if present in the starting material or formed during heating, somehow, appear on the surface of the specimen after microwave treatment. [ABSTRACT FROM AUTHOR]