X-Ray Study of Phase Transition in NaClO₄

Abstract

The phase transition in NaClO₄ from the NaCl-type cubic phase (O_h⁵) to the orthorhombic phase (D_2h¹⁷) is investigated with X-ray diffraction method. In the cubic phase, X-ray diffuse maxima are observed at the X-points of the Brillouinzone boundary. The intensity of the diffuse maximum anomalously increases with decreasing temperature toward the transition point. In the orthorhombic phase, the intensity of the super lattice reflection sharply decreases near the transition point and the lattice constant b shows anomalous expansion with increasing temperature. It is suggested that a coupling between multi-orientation of ClO₄⁻ ion and phonon plays an important role in the phase transition.