Structural Peculiarities and Thermoelectric Study of Iron Indium Thiospinel

The homogeneity range of ternary iron indium thiospinel at 873 K was investigated. A detailed study was focused on two distinct series (y=z): 1) a previously reported charge‐balanced (In0.67+0.33y□0.33−0.33y)tetr[In2−zFez]octS4 (A1‐series; □ stands for vacancy; the abbreviations “tetr” and “oct” indicate atoms occupying tetrahedral 8a and octahedral 16d sites, respectively) and 2) a new charge‐unbalanced (In0.67+y□0.33−y)tetr[In2−zFez]octS4 (A2‐series). Fe atoms were confirmed to exclusively occupy an octahedral position in both series. An unusual reduction of the unit cell parameter with increasing Fe content is explained by differences in the ionic radii between Fe and In, as well as by an additional electrostatic attraction originating from charge imbalance (latter only in A2‐series). The studied compound is an n‐type semiconductor, and its charge carrier concentration increases or decreases for larger Fe content within the A1‐ and A2‐series, respectively. The thermal conductivity κtot is significantly reduced upon increasing vacancy concentration, whereas the change of power factor is insufficient to drastically improve the thermoelectric figure of merit. Iron indium thiospinel: Two different mechanisms for the Fe incorporation into indium thiospinel were investigated, namely the charge‐balanced (A1) and the charge‐unbalanced (A2) series. The Fe content (i.e., vacancy concentration) strongly influences the unit cell parameter, charge carrier concentration, charge carrier mobility, as well as thermal conductivity (κtot) in both series.