Charge ordering in Sm₄Bi₃ under pressure

We have investigated the charge ordering in Sm₄Bi₃ under pressure by magnetic susceptibility and x-ray diffraction measurements. We observed discontinuous anomalies in the temperature dependences of magnetic susceptibility and volume at the charge ordering transition owing to the first-order transition and then the estimated charge ordering transition temperature decreases linearly with increasing pressure. The volume ratio between the SmBi₆ octahedra at two nonequivalent Sm sites indicates the partial charge ordering of Sm ions in the charge ordered phase. The evidence of the partial charge ordering in Sm₄Bi₃ is consistent with the smaller electronic component in the entropy change at the charge ordering transition.