The solid solution series Ge12M2Te15 (M = Sb, In): Nanostructures and thermoelectric properties

• A new solid solution series of rocksalt-type Ge12M2Te15 (M = Sb, In) is described.
• Up to 300 °C, In substitution increases Seebeck coefficients and ZT values.
• Phase transitions influenced by the In content determine the real structure.
• TEM images reveal pronounced nanostructures with intersecting defect layers.
• Lower temperature of cubic-trigonal phase transition upon In doping is beneficial.

Quenching rocksalt-type high-temperature phases of members of the solid solution series Ge12M2Te15 (M = Sb, In) results in nanostructured (pseudo-)cubic materials as shown by high-resolution electron microscopy. The transition temperatures between the thermodynamically stable trigonal phases and the cubic high-temperature phases decrease with increasing In content. Due to a pronounced increase of the Seebeck coefficient, the thermoelectric figure of merit (ZT) of Ge12SbInTe15 (average structure: Fm3¯m,a = 5.9603(1), RBragg = 0.024) is higher than that of Ge12Sb2Te15 up to 300 °C. This effect is even more pronounced for metastable Ge12In2Te15 (average structure: Fm3¯m,a = 5.94723(4), RBragg = 0.048).

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