Phase Formation Behavior and Thermoelectric Transport Properties of Solid Solution Composition Between SnTe and InTe

Alloys based on SnTe have been widely studied for their eco-friendly characteristics and good electrical performance in the high-temperature range above 600 K. In this study, SnTe-InTe solid solution alloy compositions of Sn_{1 − x}In_xTe (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) were investigated for their phase formation behavior and thermoelectric properties. A single cubic SnTe phase was formed in x ≤ 0.4 samples, while x = 0.6 and 0.8 samples formed multi-phase with a tetragonal InTe phase. The carrier mobility gradually decreased with increasing x in the single cubic phase region (x = 0-0.4), and a drastic reduction of 58% for x = 0.2 and 82% for x = 0.4, causing S and σ to decrease simultaneously compared to that of the pristine SnTe. Thus, the power factor gradually reduced to 0.06 mW/mK² for x = 0.4 compared to 1.57 mW/mK² for the pristine sample, as confirmed by the weighted mobility reduction behavior. The lattice thermal conductivity showed a gradual decrease in the simple cubic phase region, owing to the additional point defects formed by In substitution of Sn sites. Consequently, zT gradually decreased from 0.31 for the pristine to 0.02 for x = 0.4 sample due to the degradation of carrier transport properties, specifically Hall mobility, outweighing the total thermal conductivity reduction. The maximum zT value of 0.50 at 750 K was observed for InTe (x = 1.0). Additional analysis using the single-parabolic-band model indicated that zT enhancement through carrier concentration optimization was not feasible for the alloy samples.