Influence Of Pressure And Transition Metal (T=Fe,Co) On The Lanthanum Bare Frequency In Lat4sb12

In this paper we explore, by means of first-principles calculations, the influence of pressure and transition-metal (T=Fe,Co) on the structure and lanthanum bare frequency in LaFe4Sb12 and LaCo4Sb12. The guest ion bare frequency decreases almost linearly with the La-Sb distance. Substitution of Fe for Co in the framework structure promotes a reduction in the La bare frequency from around 98 to 76 cm(-1) at 0 GPa. Accordingly, the influence of the transition metal on the La bare frequency is thus an indirect effect of the former on the equilibrium La-Sb distance. A pressure increase to 1 GPa changes the guest bare frequency by 3.1 cm(-1) and 2.2 cm(-1) for LaFe4Sb12 and LaCo4Sb12, respectively. The measurable effect of pressure on the La bare frequency and, consequently, on La atomic displacement parameter, points to the possibility of using even moderate pressures to tune the guest rattling mode amplitude and controllably explore the resulting effect on the lattice thermal conductivity of ternary skutterudites and other similar open framework thermoelectric materials.