The transition from spinel-type structure to rocksalt-type structure in the compound CdHo2S4, as observed by electron microscopy/diffraction

At a temperature above 1173 K the spinel-type structure of CdHo₂S₄ becomes unstable and gradually transforms into a rocksalt-type structure. During transition both Cd²⁺ and Ho³⁺ cations shift. Electron diffraction patterns obtained during transition show that the Cd, which shifted from a tetrahedral to an octahedral site, distorts the sulfur lattice. This distortion becomes visible as a modulation of the sulfur matrix. The modulation originally occurs in many crystallographic directions, however, upon annealing the 〈111〉 direction becomes preferred. Small domains of the high-temperature structure of CdHo₂S₄ appear to occur also in samples that were annealed well below 1173 K for a long period.