Structural transformation on the pressure-induced metal-insulator transition in PrFe₄P₁₂

We report the first X-ray diffraction experiments of PrFe₄P ₁₂ under high pressure. We discovered a symmetry lowering from cubic to orthorhombic or lower at the metal-insulator transition temperature, accompanied by a jump in the lattice constant, which indicates a first-order phase transition. The superlattice reflections at q = (1, 0 0) observed in the low-pressure nonmagnetic ordered phase are found to disappear in the insulating phase. The temperature dependence of the lattice constant and the absence of the superlattice reflections are well explained by taking into account an antiferromagnetic ordering.