Charge-density-wave ordering in the metal-insulator transition compound PrRu4P12

X-ray and electron diffraction measurements on the metal-insulator (M-I) transition compound PrRu{sub 4}P{sub 12} have revealed a periodic ordering of charge density around the Pr atoms. It is found that the ordering is associated with the onset of a low temperature insulator phase. These conclusions are supported by the facts that the space group of the crystal structure transforms from Im3 to Pm3 below the M-I transition temperature and also that the temperature dependence of the superlattice peaks in the insulator phase follows the squared BCS function. The M-I transition could be originated from the perfect nesting of the Fermi surface and/or the instability of the f electrons.