Multitemperature crystal structures and physical properties of the partially filled thermoelectric skutterudites M0.1Co4Sb12(M = La, Ce, Nd, Sm, Yb, and Eu)

作者：Mi Jian Li^*; Christensen Mogens; Nishibori Eiji; Iversen Bo Brummerstedt

来源：Physical Review B, 2011, 84(6): 064114.

DOI：10.1103/PhysRevB.84.064114

Partially filled skutterudites with nominal compositions of M0.1Co4Sb12 (M = La, Ce, Nd, Sm, Yb; and Eu) were investigated by multitemperature (90-700 K) synchrotron radiation powder x-ray diffraction (SR-PXRD), and electrical and thermal transport property, heat capacity, and Hall effect measurements were also taken. The filling fractions, i.e., the occupancy factors of the guest atoms, were obtained from structure refinement of the SR-PXRD data, and they reflect the capacity for the individual guest atom species to fill the voids of the CoSb3 structure. The filling fraction of the lanthanide guest ions correlates with their effective ionic radii and valences, and the larger the ionic radii or the lower the charge state, the larger is the occupancy. Due to the different guest atom occupancies, the doping levels vary among the samples, and they are in a good agreement with the measured charge carrier concentrations, except for the magnetic samples (Sm, Eu). Anomalously large atomic displacement parameters (ADPs) are observed for the weakly bonded guest atoms, in agreement with the "rattling" concept, but no correlation is observed between the magnitude of the ADP and the ionic radius of the guest atom. Einstein and Debye temperatures were derived from analysis of the multitemperature ADPs of guest atoms and the framework atoms, respectively, and this analysis also shows that neither the guest atoms nor the host structure atoms contain large disorder contributions to their ADPs. In ternary skutterudites without host structure substitution or disorder, partial guest filling can affect the lattice thermal conductivity (kappa(L)) either by direct phonon-phonon interaction or through the inherent structural disorder introduced with the partial occupancy of the voids. The present data suggest that the magnitude of the guest atom ADPs correlates with kappa(L), and the larger the ADP, the lower is the kappa(L).

• 出版日期2011-8-24