Basic thermoelectric p‐type materials for the medium temperature range (600 to 900 K) are GeTe‐based materials. Hot‐pressed samples of (GeTe)1−x[(Ag2Te)1‐y(Sb2Te3)y]x solid solutions with y = 0.6, y = 0.75 are prepared. Their thermoelectric properties (thermoelectric power S, electric conductivity σ and thermal conductivity K) in the temperature range 300 to 750 K are measured. The thermoelectric figure of merit Z = S2σ/K for some compositions in calculated. The best p‐type new material is the composition (GeTe)0.8[(Ag2Te)0.4(Sb2Te3)0.6]0.2 with Zmax = 2.4 × 10−3 K−1 at about 700 K.

The thermoelectric power S of GeTe‐rich (GeTe)1‐x(Bi2Te3)x solid solutions (0 ≦ x ≦ 0.05) is investigated as a function of composition x and temperature T in the range from 80 to 350 K, where the materials have the crystal and band structure of the rhombohedral α‐phase of GeTe. On the basis of the non‐parabolic two‐band Kane model of IV‐VI compounds information on the Fermi energy F (reduced Fermi energy F* = F/k0T, where k0 is the Boltzmann constant) and the degeneracy of the alloys is deduced. A qualitative interpretation of the temperature and composition dependences of S is made. It is assumed that there are two types of carriers (light and heavy holes) and redistribution among the valence bands with the change of temperature.

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The calculation of transport effects requires both the knowledge of some intrinsic material parameters (deformation potentials, effective masses, impurities potential well strength, etc. ) and the values of integrals, which as a rule cannot be represented by elementary functions. When a relaxation time for the carrier scattering r can be introduced, these integrals a r e of the formwhere fo is the Fermi-Dirac distribution function, and E, k(E), and m(E) are the energy, the wave number, and the effective mass of the carriers with a relevant energy dependence determined by the adopted energy dispersion law.When narrow band-gap semiconductors are concerned and Kane-type band is applicable, and on the assumption that the relaxation time depends on energy only through the density of energy states, one readily obtains the so-called generalised Fermi-Dirac integralswhere z = E KT, p= kT/E , and x = E/kT a r e the reduced Fermi energy, the non-parabolicity parameter and the dimensionless energy of the carriers (E is the band gap). These integrals were calculated by Zawadski et al. /2/ and listings for some values of z and B can be found in /3/. When p + O these integrals reduce to the ordinary Fermi-Dirac integrals, corresponding to a parabolic energy dispersion law, according to /4/

Electrical conductivity o, Hall coefficient R H , arid thermoelectric power (Scebeck coefficient) S are measured for (GeTe)l-.(Bi2Te3)z solid solutions with 0 5 z 5 0.05 in the temperature range 80 to 350 K. On the basis of these investigations some information on the carrier scattering mechanisms in the alloys is obtained. The electrical resistivity e = l/o is analyzed as function of temperature T and composition z in the above-mentioned temperature interval and resistivity contributions due to acoustic phonori scattering (eat) and to scattering by defects (germanium vacancies, impurity atoms, etc.) and alloy scattering are distinguishcd. From the rcsults it may bc shown that the acoustic phonon resistivity increases nearly linearly with temperature. At low temperatures the resistivity due to defects edef is almost constant and slowly increases at temperatures T > 250 K.