Publication Date:
2016-04-20
Description:
We examined the crystal structure of the new thermoelectric material LaOBiS 2− x Se x , whose thermoelectric performance is enhanced by Se substitution, by using powder synchrotron X-ray diffraction and Rietveld refinement. The emergence of metallic conductivity and enhancement of the thermoelectric power factor of LaOBiS 2− x Se x can be explained with the higher in-plane chemical pressure caused by the increase of Se concentration at the in-plane Ch1 site (Ch = S, Se). High-temperature X-ray diffraction measurements for optimally substituted LaOBiSSe revealed anomalously large atomic displacement parameters ( U iso ) for Bi and Ch atoms in the BiCh 2 conduction layers. The anisotropic analysis of the atomic displacement parameters ( U 11 and U 33 ) for the in-plane Bi and Ch1 sites suggested that Bi atoms exhibit large atomic displacement along the c -axis direction above 300 K, which could be the origin of the low thermal conductivity in LaOBiSSe. The large Bi vibration along the c -axis direction could be related to in-plane rattling, which is a new strategy for attaining low thermal conductivity and phonon-glass-electron-crystal states.
Print ISSN:
0021-8979
Electronic ISSN:
1089-7550
Topics:
Physics
