A high-pressure route to thermoelectrics with low thermal conductivity: The solid solution series AgInxSb1−xTe2 (x=0.1–0.6)

Metastable rocksalt-type phases of the solid solution series AgInxSb1−xTe2 (x=0.1, 0.2, 0.4, 0.5 and 0.6) were prepared by high-pressure synthesis at 2.5 GPa and 400 °C. In these structures, the coordination number of In3+ is six, in contrast to chalcopyrite ambient-pressure AgInTe2 with fourfold In3+ coordination. Transmission electron microscopy shows that real-structure phenomena and a certain degree of short-range order are present, yet not very pronounced. All three cations are statistically disordered. The high degree of disorder is probably the reason why AgInxSb1−xTe2 samples with 0.4<x<0.6 exhibit very low thermal conductivities with a total κ<0.5 W/K m and a lattice contribution of κph ∼0.3 W/K m at room temperature. These are lower than those of other rocksalt-type tellurides at room temperature; e.g. the well-known thermoelectric AgSbTe2 (κ ∼0.6 W/K m). The highest ZT value (0.15 at 300 K) is observed for AgIn0.5Sb0.5Te2, mainly due to its high Seebeck coefficient of 160 µV/K. Temperature-dependent X-ray powder patterns indicate that the solid solutions are metastable at ambient pressure. At 150 °C, the quaternary compounds decompose into chalcopyrite-type AgInTe2 and rocksalt-type AgSbTe2. - Graphical abstract: Reaction scheme, temperature characteristics of the ZT value and a selected-area electron diffraction pattern (background) of AgIn0.5Sb0.5Te2, which crystallizes in a rocksalt-type structure with statistical cation disorder. Display Omitted - Highlights: • High-pressure synthesis yields the novel solid solution series AgInxSb1−xTe2. • In contrast to AgInTe2, the compounds are inert at ambient pressure. • HRTEM shows no pronounced short-range order in the disordered NaCl-type structure. • The metastable phases exhibit very low total thermal conductivities <0.5 W/K m. • ZT values of 0.15 at room temperature were measured for AgIn0.5Sb0.5Te2