@article{oai:u-ryukyu.repo.nii.ac.jp:02011296,
 author = {Suekuni, K. and Avila, M. A. and Umeo, K. and Fukuoka, H. and Yamanaka, S. and Nakagawa, T. and Takabatake, T.},
 issue = {23},
 journal = {Physical Review B},
 month = {Jun},
 note = {We report structural, transport, and thermal properties of carrier-tuned Ba_8Ga_<16>Sn_<30> single crystals with the type-1 clathrate structure (β phase), demonstrating that Ba_8Ga_<16>Sn_<30> is a unique thermoelectric clathrate material wherein both the structure type and the carrier type are tunable. The results are compared with the properties of the better known type-8 structure (α phase) and of A_8Ga_<16>Ge_<30> (A=Sr,Eu). Differential thermal analysis and powder x-ray diffraction show that both phases are stable up to their virtually identical melting point of 520±3 °C. Refinements of single-crystal x-ray diffraction data indicate that the Ba(2) guest ion in the tetrakaidecahedron occupies the off-center 24k sites which are 0.43–0.44 Å away from the centered 6d site. The temperature-linear coefficient of the specific heat is 29 mJ/mol K^2 for both n- and p-type carriers in the β phase, four times larger than that for the α phase, suggesting contributions from tunneling of the Ba(2) guest ions between off-center minima. Analysis of specific heat with a soft-potential model (SPM) gives a characteristic energy of 20 K for the Ba(2) vibration, significantly lower than 50 K for the α phase and in fact the lowest among type-1 clathrates. The lattice thermal conductivities κL for the β phase with both charge carrier types are very similar and show a glasslike temperature dependence. This behavior in κL(T) is also described using SPM analysis, where it is found that the coupling strength between guest modes and acoustic phonons for the β phase is significantly larger than that for Sr_8Ga_<16>Ge_<30>., 論文},
 title = {Simultaneous structure and carrier tuning of dimorphic clathrate Ba_8Ga_<16>Sn_<30>},
 volume = {77},
 year = {2008}
}