Charge-ordering in Sm₄Bi₃ and Yb₄As₃ with the anti-Th₃P₄ structure

Sm₄Bi₃ and Yb₄As₃ are mixed valence materials with the ratio of 1:3 of trivalent and divalent rare earth ions and are expected to show charge-ordering. In the specific heat of Sm₄Bi₃ and Yb₄As₃ we observed very sharp peaks at 260 K and at 293 K, respectively. Entropies estimated from these peaks are too small to be ascribed to full ordering, suggesting short range ordering at higher temperatures.