Elastic Constants of Filled Skutterudite LaRu₄As₁₂

Ultrasonic measurements with frequencies varying between 73 and 160 MHz were performed for the LaRu₄As₁₂ single crystal. This As-based filled skutterudite compound is a BCS-type superconductor with T_sc as high as 10.3 K. In order to examine a presence of off-center rattling motion in LaRu₄As₁₂, we measured elastic constants C_L111 = (C₁₁ + 2C₁₂ + 4C₄₄)/3 and C_T111 = (C₁₁ – C₁₂ + 4C₄₄)/3, which are related to longitudinal and transverse sound waves propagating along the [111] direction, respectively. No ultrasonic dispersion was found in the whole temperature range from 1.4 to 300 K.