Structural Investigation and Indium Substitution in the Thermoelectric Mn_2.7Cr_0.3Si₄Al_2−xIn_x Series

Following the recent discovery of the promising Mn_2.7Cr_0.3Si₄Al₂ thermoelectric compound (having, e.g., automotive, industrial, and solar conversion applications), structural characterization by x-ray single-crystal diffraction analysis has been performed. This layered material is composed of two distinct crystallographic sites where both (Mn, Cr) and (Al, Si) are randomly distributed. The deduced crystallographic parameters were then confirmed by powder x-ray diffraction analysis through a temperature dependence of the phase stability, showing at the same time chemical stability up to 873 K. Taking into account the two distinct crystallographic sites highlighted, samples possessing two guest elements, one on each site, were then synthesized to improve the thermoelectric properties. A solid solution is found in the system Mn_2.7Cr_0.3Si₄Al_2−xIn_x with x varying from 0 to 0.2. Thus, double-substituted samples were studied by x-ray diffraction, electrical, and thermal measurements. The present paper describes and discusses the experimental results obtained.