Shock-induced phase change in BaZnGeO4 crystals

Shock-loading experiments are performed on single-crystal specimens of BaZnGeO₄ (BZG) between 13 and 51 GPa using a propellant gun and a two-stage light gas gun. Observation by an optical microscope reveals that all the shocked specimens are made of fragmented blocks of 10 ～ 100 μm in size. X-ray analyses indicate that the samples shocked to pressures above 41 GPa became a polycrystalline state of BZG with a weakly textured structure. A small amount of dissociation products of BaGeO₃ (pyroxene type) and ZnO (wurtzite type) are detected in this pressure range. Between 27 and 19 GPa, a new phase which is thought to be produced by considerable deformations in the ring structure consisting of ZnO₄ and GeO₄ tetrahedra is observed. Below 19 GPa, shocked specimens are brought into a well aligned mosaic structure, but no significant change in the crystal structure is detected.