Structural Phase Transitions and Thermoelectric Properties of AgPb18SbTe20 Under Compression

The high-figure-of-merit thermoelectric material AgPb₁₈SbTe₂₀ has been investigated by in situ angular-dispersive x-ray diffraction (XRD) and x-ray absorption fine-structure (XAFS) measurements up to 30 GPa. Resistivity and thermopower were measured with Bridgman-type opposed metal anvil cells. The results show that the ambient cubic ( Fm[`3] m ) left( {Fmoverline{3} m} right) structure transforms to orthorhombic (Pnma) at 6.4 GPa and then to the CsCl-type ( Pm[`3] m ) left( {Pmoverline{3} m} right) structure at 15 GPa. The ambient cubic ( Fm[`3] m ) left( {Fmoverline{3} m} right) phase is found to be recoverable on releasing the pressure. The thermoelectric power is found to increase with pressure for the cubic phase. The XAFS studies performed at the Pb L ₃-edge and Ag K-edge along with resistivity studies complement the XRD findings.