Pressure induced structural changes in AgPb18SbTe20*

The cubic chalcogenide AgPbmSbTe2+m type compounds are an important class of thermoelectric materials for which figures of merit as high as 2.2 at 800 K have been reported recently [1]. The structures of these compounds have been investigated under pressures up to 30 GPa using a diamond-anvil cell and an imaging plate with synchrotron radiation at HPCAT. Various runs were performed with different pressure media such as 4:1 methanol-ethanol and silicone fluid. The results show pressure induced structural transitions in AgPb18SbTe20. The NaCl-type cubic phase transforms to an orthorhombic phase at 6.4 GPa and then to a CsCl-type cubic structure at 14 GPa. The high pressure CsCl-type phase is stable up to 30 GPa. The ambient structure is recovered on releasing the pressure from the cell. The results will be presented in detail. [1]. K.F. Hsu etal., Science, 303, 818 (2004)