| Research Abstract |
Filled skutterudite compounds are represented as RT_4X_<12> (R=alkali,alkaline-earth,rare-earth;T=Fe,Ru,Os;X=P,As,Sb) and the atomic positions are the followings : R in 2a (0,0,0),T in 8c (1/4,1/4,1/4) and X in 24g (0,u,v). We call u and v internal parameters.
We have already reported that the crystal electric fields at R site have the new term O_<6^2>-O_<6^6> due to the cubic point group T_h. In order to investigate the internal parameter dependence, we derive an analytic representation for the coefficient of new term as a function of u and v using the point charge model.
We have already reported the electronic band structures for binary skutterudites T'X_s (T'=Co,Rh, Ir;X=P,As,Sb). We get narrow gap semiconductors, zero-gap semiconductors and typical semimetals depending on elements. We fined that results are classified by the values of u and v. Then we calculate the electronic band structures of CoAs_3 with hypothetic sets of u and v, and get consistent results with our classification
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Band structure calculations for the ferromagnetic Eu-,Yb-, alkaline-earth- and Na-based skutterudites are carried out using the FLAPW method with LSDA. We get the stable ferromagnetic solution for Fe-Sb skutterudites because the Fe 3d state has more localized character and the Fe 3d levels of Fe-Sb skutterudite are the shallowest.
PrRu_4P_<12> has been known to show a metal-insulator transition at 60 K with structural transformation from a bcc structure (the high-temperature phase) to a simple cubic one (the low temperature phase). In the low temperature insulator phase, local environments around the Pr ions at the unit cell origin and at the body center in the bcc structure are different. Then two crystal field schemes for each Pr ion sites are reported. The electric band structure is calculated for LaRu_4P_<12> with the simple cubic PrRu_4P_<12> crystal structure. We investigate the hybridization between the La f-orbital and the P-p state and get that the p-f hybridization has the selection rule depending on sites. This selection rule is considered to be one of origins of different crystal field schemes of Pr sites. Less
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