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 Pm3 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].