Indium thiospinel In_1−x□_xIn₂S₄ – structural characterization and thermoelectric properties

Abstract

Structural disorder induced by β↔α polymorphic transformation strongly affects electronic and thermal transport in indium thiospinel.

Structural Peculiarities and Thermoelectric Study of Iron Indium Thiospinel

“… Unit cell parameters (UCPs) versus M /In ratio of samples from the A1‐ and A2‐series after synthesis as well as previously reported data . M =Fe or In (excess of In in comparison with composition In 0.67 □ 0.33 In 2 S 4 , only for binary samples). Numbers indicate the Fe content per respective formula unit.…”

“…Further decrease of x (i.e., incorporation of additional In atoms in the structure) leads to a charge imbalance in this thiospinel. The charge imbalance in turn can cause additional electrostatic attractions between In 3+ and S 2− ions within the tetrahedra, which then results in a shortening of In−S contacts (Table ) and thus in the decrease of UCPs . A similar phenomenon was observed for ZrO 2− x and CeO 2− x …”

“…PXRD phase analysis clearly indicates that incorporation of a small amount of iron into the initially tetragonal In 0.67 □ 0.33 In 2 S 4 (the β polymorph) leads to a stabilization of the cubic MgAl 2 O 4 structure type ( Fd m , a ≈10 Å, Figure a) for the studied thiospinels. The unit cell parameter (UCP) decreases monotonously for larger Fe content (lower vacancy concentration) in both sample series (in agreement with the previous report, Figure ).…”

“…No changes in UCPs for both series were observed after spark plasma sintering (SPS) and high‐temperature (HT) transport measurements (LFA, ZEM‐3), thus indicating the thermal stability of the materials. Reduction of UCP for lower vacancy concentration, observed also for binary In 1− x □ x In 2 S 4 thiospinel, is an unusual effect and there is no solid explanation for it so far.…”

“…Recent studies revealed that even the binary In 1− x □ x In 2 S 4 ( x =0.33) thiospinel (□ stands for vacancy) presents a promising TE figure of merit ZT between 0.2–0.4 above 700 K. The further incorporation of In in the compound (i.e., x =0.22 and 0.16) is accompanied with an enhancement of structural disorder (which promotes an intrinsically low thermal conductivity κ tot <0.5 W m −1 K −1 above RT), as well as with a reduction of the charge carrier concentration ( n <10 18 cm −3 at 298 K) leading to a decrease of the ZT parameter . Seemingly, the simplest way to improve TE efficiency (i.e., to enhance n ) of the In 1− x □ x In 2 S 4 thiospinel would be an incorporation of the third element into its structure.…”