X-Ray Study on the Successive Phase Transitions of K₂CoCl₄

Abstract

The structural phase transition of K₂CoCl₄ is investigated by means of X-ray scattering. The transition temperatures are 558 K, 454 K and 142 K. With decreasing temperature, the symmetry of the crystal changes as follows: phase I, normal [Pmcn]; phase II, incommensurate [q=(1⁄3−δ)c^*]; phase III, commensurate [P2₁cn, q=c^*⁄3]; and phase IV, commensurate [C1c1, q=a^*⁄2+b^*⁄2+c^*⁄3]. Here the reciprocal vectors refer to the normal phase. In a narrow temperature range just above 142 K, the superreflection at (5/2 3/2 0) splits into two diffuse peaks. The general feature of the successive transitions is very similar to K₂ZnCl₄.