Phase transition effects in polycrystalline Hg2Br2 samples

The effects accompanying the ferroelastic phase transition in Hg2Br2 polycrystalline samples are compared in an x-ray diffraction study with similar effects observed to occur in Hg2Br2 single crystals. In particular, an analysis is made of the “orthorhombic” splitting of the basal plane reflections and the behavior with temperature of the Bragg and diffuse reflections from the X points of the Brillouin zone, which characterize the behavior of the order parameter and its fluctuations, respectively. Polycrystalline samples exhibit strong smearing of the phase transition effects originating from the existence of damaged surface layers and elastic and plastic strain fields which induce order parameter fluctuations over a wide temperature range.