Elastic properties of the filled and unfilled skutterudite compounds

Abstract

Ultrasonic measurements were made on a single crystal of the unfilled skutterudite compounds RhSb3 and IrSb3 and compare with that of the filled skutterudite PrOs4 Sb12 to elucidate the role of the guest ions Pr. A characteristic increase was observed around 30 K in the temperature dependence of elastic constants (C11-C 12)/2 and C44 which is ascribed to unusual vibration "rattling" of Pr ions in an atomic cage formed by Sb-icosahedron. On the other hand, the elastic constants C11, (C11-C 12)/2 and C44 increase monotonically with decreasing temperature in the case of RhSb3 and IrSb3. No such a characteristic increase was observed. These results give us a piece of evidence that the guest ions would play a crucial role for "rattling motion" in filled skutterudite compounds. © 2007 IOP Publishing Ltd.