Structural Phase Transition Accompanied by Metal - Insulator Transition   in PrRu4P12
  A structural phase transition has been found using electron diffraction technique in PrRu4P12 accompanied by a metal - insulator (M - I) transition (TMI = 60K). Weak superlattice spots appeared at (H, K, L) (H + K + L = 2n + 1; n is an integer) position at a temperature of T = 12 K and 40 K. Above T = 70 K, the spots completely vanished. The space group of the low temperature phase is probably Pm3. This is the first observation of a symmetry other than Im3 in skutterudite compounds. 
C. H. Lee, H. Matsuhata, A. Yamamoto, T. Ohta, H. Takazawa, K. Ueno,   C. Sekine, I. Shirotani and T. Hirayama