Journal of Materials Science Research and Reviews

Maximization of the Figure of Merit of Alloy Si\(_x\)Ge\(_{1-x}\)

Irakli Nakhutsrishvili *

Institute of Cybernetics of Georgian Technical University, Georgia.

Zurab Adamia

Tbilisi State University, Georgia and University of Georgia, Georgia.

Giorgi Kakhniashvili

Institute of Cybernetics of Georgian Technical University, Georgia.

*Author to whom correspondence should be addressed.

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Abstract

The dependence of maximums of figure of merit ((ZT)_max) on thermoelectric quality factor (B) for thermoelectric Si_xGe_1-x of n- and p-type conductivity with a charge carrier concentration of 3.210²⁶m^-3 has been considered. The values of x are: 0.7, 0.72, 0.76, 0.8 and 0.83. For all samples, (ZT)_max appears at about 900°C. The (ZT)_max– σ' (universal electrical conductivity) dependence allows us to assume with sufficient accuracy the mentioned maxima for other values of σ' (that is, for Si_xGe_1-x with other relative compositions as well. Thus, σ' can be used to predict of (ZT)_max. With this approach, a coefficient of thermal conductivity (k_L) is not required. σ'S² – S  dependence is also considered (S – Seebeck coefficient). Experimental points and the averaged curve for a large number of samples calculated from the data of literature match well. The middle part of this dependence (1^.10^-4\(\le\)S \(\le\) 2.5^.10^-4 V^.K^-1) is well described by the parabolic empirical expression. And in the range 0\(\le\) S\(\le\) 6^.10^-4V^.K^-1 the equation of exponential type should be used. Experimental points in coordinates σ'- B_S/S²(B_S=σS²/B_E, σ - specific electrical conductivity, B_E – electronic quality factor) are well located on a straight line for all x in n- and p-Si_xGe_{1-x ,}except for some points for p-Si_0.7Ge_0.3. The dependence σ'- B_S/S² have the form of a straight line with a slope of 1.34710⁸ SimW^-1K^-2.

Keywords: Thermoelectric SiGe, maximums of figure of merit, electrical conductivity

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