Nanostructures versus Solid Solutions: Low Lattice Thermal Conductivity and Enhanced Thermoelectric Figure of Merit in Pb9.6Sb0.2Te10-xSex Bulk Materials

The series of Pb9.6Sb0.2Te10-xSex compounds with different Se content (x) were prepared, and their structure was investigated at the atomic and nanosized regime level. Thermoelectric properties were measured in the temperature range from 300 to 700 K. The Pb9.6Sb0.2Te10-xSex series was designed after the refinement of the single-crystal structure of Pb3.82Sb0.12Te4 (Pb9.6Sb0.3Te10; S.G. Pm3m) by substituting isoelectronically in anion positions Te by Se. The Pb9.6Sb0.2Te10-xSex compounds show significantly lower lattice thermal conductivity (κL) compared to the well-known PbTe1-xSex solid solutions. For Pb9.6Sb0.2Te3Se7 (x = 7), a κL value as low as 0.40 W/m·K was determined at 700 K. High-resolution transmission electron microscopy of several Pb9.6Sb0.2Te10-xSex samples showed widely distributed Sb-rich nanocrystals in the samples which is the key feature for the strong reduction of the lattice thermal conductivity. The reduction of κL results in a significantly enhanced thermoelectric figure of merit o...