G. N. Isachenko

Transport properties of Mg2 X 0.4Sn0.6 solid solutions (X = Si, Ge) with p-type conductivity

The transport properties of Mg2X0.4Sn0.6 (X = Si, Ge) solid solutions are investigated. It is shown that these materials can be rendered p-type with a hole concentration of up to 4 × 1019 cm−3. The Hall coefficient, thermopower, and electrical conductivity are measured over a wide temperature range. The mobility of holes in these solid solutions is less than that of electrons by a factor of 2 for Mg2Si0.4Sn0.6 and by a factor of 1.5 for Mg2Ge0.4Sn0.6. Solid solutions in the Mg2Ge-Mg2Sn system appear more promising for thermoelectric applications.

Kinetic properties of p-Mg2SixSn1 − x solid solutions for x < 0.4

The results of a study of Mg2SixSn1 − x solid solutions (x = 0.25, 0.3, 0.35, 0.4) are reported. The measurements performed cover the Seebeck coefficient, electrical conductivity and the Hall coefficient over broad ranges of temperatures (80–700 K) and carrier concentrations (1018 to 6 × 1020 cm−3). These measurements were used to derive the band structure parameters (band gap, hole mobility, hole effective mass). The effective mass of holes was found to grow strongly with an increase in their concentration.

Influence of heat treatment on the structure and thermoelectric properties of CrSi2

Textured CrSi2 crystals obtained by heating finely dispersed constituents (Si, Cr) are studied. The use of a mixture of Cr and Si powders makes it possible to lower the CrSi2 synthesis temperature by 100 K. Crystallization conditions and post-crystallization annealing are found to influence the thermoelectric properties and composition of samples.

Kinetic properties of p-type Mg/sub 2/Ge/sub 0.4/Sn/sub 0.6/ solid solutions

In this paper the results of the study of kinetic properties of the Mg/sub 2/Si/sub 0.4/Sn/sub 0.6/ solid solution are presented. It is shown that it is possible to produce the Mg/sub 2/Si/sub 0.4/Sn/sub 0.6/ solid solution with of p-type with various hole concentration (up to 4 /spl middot/ 10/sup 19/cm/sup -3/). Seebeck and Hall coefficients and electrical conductivity were measured in the temperature range 100 - 800 K. The hole mobility in these solid solutions is lower than that of electrons. Some parameters of valence band are determined.

Application of the solution–melt method for obtaining composite materials consisting of a metal matrix and CrSi2 microcrystals

The possibility of obtaining composite materials in which the metal matrix is filled with CrSi2 needle microcrystals is considered. It is shown that it is possible in principle to obtain a regular structure of CrSi2 microcrystals in metal matrices of tin, aluminum, and their alloys. During chemical etching, a part of the matrix volume is dissolved, releasing “rods” of the semiconducting material. The thermoelectric parameters of such a system are estimated on the basis of the measured physical properties.

Homogeneity domain and thermoelectric properties of CrSi2

The phase composition, structure, and thermoelectric properties of CrSi2 obtained by low-temperature synthesis are investigated. The results indicate the strong effect of the silicon sublattice on the thermoelectric properties of the material and the possibility of solid-phase low-temperature transformations in a CrSi2 crystal lattice.

Crystallization and properties of CrSi2 single crystals grown from a tin solution-melt

Using the solution-melt method combined with the Bridgman method, CrSi2 single-crystal needles and single-crystal tubes are grown at a temperature lower than their melting (crystallization) temperature. Microcrystals thus grown feature an anomalously high thermal emf. The growth of CrSi2 single-crystal tubes is an important step forward in the production of various devices based on high-temperature thermoelectric materials.

Crystallization of highest manganese silicide MnSi1.71-1.75 from tin-lead solution-melt

A new version of controlled synthesis of single-crystal and textured highest manganese silicide (HMS) MnSi1.71–1.75 is considered. This thermoelectric crystallizes on the surface of molten metals (Sn, Pb), which forms a floating lens. Such a configuration produces a narrow oriented zone with a sharp temperature gradient (zone melting). Simultaneously, Sn and Pb serve as solvents, as a result of which HMS partially recrystallizes in the form of microcrystallites in the bulk of HMS-Sn or HMS-Pb solution-melt.

Anisotropic layered high-temperature thermoelectric materials based on the two-phase CrSi2-β-FeSi2 system

The feasibility of synthesizing a wide spectrum of multiphase microstructurally ordered high-temperature thermoelectrics with highly anisotropic thermoelectric parameters is demonstrated with an aluminum-doped CrSi2-β-FeSi2 system the composition of which varies from Cr0.1Fe0.9Si2−xAlx to Cr0.9Fe0.1Si2−xAlx (x = 0.0–0.4). Doping of either phase (CrSi2 and β-FeSi2) is viewed as a promising way for synthesizing n- and p-type domains inside the same sample.

Thermoelectric properties of the Mg2Ge0.3Sn0.7 solid solution with p-type conductivity

The thermoelectric properties of the Mg2Ge0.3Sn0.7 solid solution doped with Ga and Li are studied. The samples with a hole concentration as high as 5 × 1020 cm–3 are obtained. The temperature dependences of the thermopower, electrical conductivity, and thermal conductivity are measured in the range from room temperature to 800 K. A higher mobility of free charge carriers is observed in the samples doped with lithium than in the samples doped with gallium. The largest thermoelectric figure of merit in the samples under study amounts to 0.42 at 700 K.