Pseudoamorphization of Cs₂HgBr₄

Synchrotron-radiation diffraction experiments have revealed the critical role of nonhydrostatic stresses in the pressure-induced long-range order dissipation in Cs₂HgBr₄ crystals. With nonhydrostatic loading, the samples lose, reversibly, long-range order on the scale observable with x-ray diffraction above 11 GPa while hydrostatic conditions preserve long-range order up to 40 GPa, the limit achieved experimentally. The phenomenon is interpreted in terms of inhomogeneous lattice deformations induced in the sample by deviatoric stresses. Diffraction patterns of synthetic grains with chaotic distribution of deformations were computed, which displayed a sufficiently good agreement between calculated and observed diffraction patterns as to support the model.