TAGS-related indium compounds and their thermoelectric properties – the solid solution series (GeTe) x AgIn y Sb 1−y Te ₂ ( x = 1–12; y = 0.5 and 1)

Various members of the solid solution series (GeTe)xAgInySb1−yTe2 can be obtained by quenching high-temperature phases (x = 12 for y = 1 and x > 5 for y = 0.5). In contrast, high-temperature and high-pressure conditions (2.5 GPa, 350 °C) are required for the synthesis of members with In contents >3.6 atom% (such as x 5 adopt the α-GeTe structure type (3 + 3 coordination). Thus, in all samples investigated, 3 or 4 cations are disordered at one Wyckoff position. The quenched high-temperature or high-pressure phases, respectively, are almost homogeneous. Their powder X-ray diffraction patterns suggest pure phases; yet, high-resolution electron microscopy occasionally reveals a very small extent of nanoscopic precipitates as well as dislocations and twinning. (GeTe)5.5AgIn0.5Sb0.5Te2 shows a maximal ZT value of 0.75 even when (partial) decomposition into the TAGS material (GeTe)11AgSbTe2 and chalcopyrite-type AgInTe2 has occurred at 300 °C. (GeTe)5.5AgInTe2 prepared under high-pressure conditions exhibits a ZT value of 0.6 at 125 °C, i.e. far below the decomposition temperature and thus is an interesting new low-temperature thermoelectric material.