Phonon Dispersion and Lifetimes in the High-entropy Thermoelectric Alloy: AgSbPbSnGeTe5

PbTe, as one of the best medium temperature thermoelectric materials currently available, has been partially applied in devices. It was found that giant anharmonic phonon scattering is the microscopic origin of low lattice thermal conductivity in PbTe by inelastic neutron scattering measurements. AgSbPbSnGeTe5 is a high-entropy thermoelectric material developed on the basis of PbTe, showing a strong lattice disorder while maintaining the stability of the face centered cubic structure. In contrast to PbTe, AgSbPbSnGeTe5 shows a glass-like temperature dependent thermal conductivity, approaching amorphous limit ~0.37 W/(mK) at 673 K. Given such low thermal conductivity, AgSbPbSnGeTe5 also exhibits better figure of merits (ZT=~1.22 at 673 K) than pure PbTe. However, the origin of ultralow and glass-like lattice thermal conductivity in AgSbPbSnGeTe5 is still unknown. Compared with PbTe, high-entropy AgSbPbSnGeTe5 may or may not exhibit similar giant phonon anharmonicity, low-frequency optical phonons, the avoided-crossing phonon, and phonon softening in its phonon dispersion. Understanding how high-entropy structure affects the phonon behaviors and making a direct comparison to pure PbTe are fundamentally intriguing, which is beneficial for explaining its ultralow lattice thermal conductivity and anomalous thermal conductivity trend. Therefore, we propose to measure phonon dispersion and lifetimes of AgSbPbSnGeTe5 at varying temperatures using MERLIN, ISIS.