Inelastic Neutron Scattering Study of Sr(Ag,Zn)Sb vacancy-defective compounds

Thermoelectric materials are attracting a great many of attentions due to its ability to transfer the temperature gradients into electrical potentials. Compounds with the ZrBeSi-structure can form with a wide range of compositions and can incorporate large defect concentrations, making it a ripe space to explore structure–property relationships. The most remarkable aspect of the ZrBeSi structure is its ability to accommodate 50% vacancies on the metal-site. Our previous study of SrAgSb and SrZn0.5Sb thermoelectric compounds showed that the vacancies in SrZn0.5Sb significantly enhance lattice anharmonicity, causing a giant softening and broadening of the entire phonon spectrum and, together with defect scattering, leading to a decrease in the lattice thermal conductivity. However, it is not clear whether the anharmonicity of phonons is continuously tunable. We plan to study the evolution of phonon anharmonicity by designing a stepwise increase in the vacancy concentration. Here, we synthesized a series of SrAg1-2xZnxSb (x=0, 0.125, 0.25, 0.375 and 0.5) vacancy-defective compounds. In this proposal, we want to apply inelastic neutron scattering technique to obtain the phonon density of states of SrAg1-2xZnxSb compounds, hence to assess the significance of vacancies in the suppression of lattice thermal conductivity.