Crystal-lattice modulation of the metal-insulator transition system PrRu4P12 studied by X-ray diffraction

PrRu₄P₁₂ exhibits a metal-insulator phase transition at T_MI=60 K. In the insulating phase below T_MI, X-ray superlattice reflections characterized by the wave vector q₀=[1,0,0] were observed. The intensities at various reciprocal-lattice positions are reproduced by a model of modulated structure with the space group Pm3̄ in which Ru and P displacements are about 0.074% and 0.06%, respectively of the lattice constant. Thus, the transition can be interpreted as the gap formation due to the nesting of Fermi surface with 2k_F=[1,0,0].