Phonon DOS of filled skutterudite, Ba0.1CoSb3

T. Kajitani1, Y. Ono1, Y. Miyazaki1, M. Sluiter2, L. Chen2*, T. Goto2,Y. Kawazoe2

1Department of Applied Physics, Graduate School of Engineering,, Tohoku University, Aoba 04, Aoba-ku,Sendai 980-8579, Japan

2Institute for Materials Research, Tohoku University, 2-1-1 Katahira-cho, Aoba-ku, Sendai 980-8577, Japan

* Present Address:Shanghai Institute of Ceramics, Chinese Academy of Science, 1295 Dingxi Rd, Shanhai 200050, China

Phonon DOS of Ba-filled skutterudite, Ba0.1CoSb3, is observed at the energy resolution of 0.1 meV (FWHM) by means of cold neutron incoherent scattering technique. Two new peaks appear at about 15 and 18 meV relative to the unfilled sample. These peaks are interpreted as Einstein-type local excitation modes of Ba-atoms based on the all-electron first-principle band calculation.. Structural relaxation of the filled skutterudite is performed during the calculation. Local deformation of CoSb8 octahedrons, i.e., the buckling of Sb-Co-Sb bond is suggested in the Ba-system, an indication of anharmonic structural response to the rattler. There are sharp Einstein peaks associated with the Ba-rattler in the 12-member cage between 2 and 3.5 THz (8.3 and 14.5 meV, respectively) in the calculated Ba-DOS curve.