High pressure structure studies of three SrGeO3 polymorphs - Amorphization under pressure

We report on the synthesis and high pressure behavior of three polymorphs of SrGeO. At ambient pressure, SrGeO crystallizes in the monoclinic structure pseudo-wollastonite. Two high pressure polymorphs, triclinic walstromite, and cubic perovskite were synthesized using a large volume multi-anvil press. The crystal structures of the three polymorphs were investigated with powder X-ray diffraction as a function of pressure using diamond anvil cells. It was found that the pseudo-wollastonite polymorph becomes amorphous at 10 GPa and equation of state fitting of the volume data yielded a bulk modulus of K = 47(4) GPa, reported for the first time. Compression of the walstromite structure showed the structure to be very compressible with two distinct phase transitions at around 10-12 GPa and 35-38 GPa. The data suggest that the structure then becomes amorphous although it retains a small degree of long-range order to the highest pressure studied. The perovskite polymorph was very incompressible and equation of state fitting of the volume data yielded a high bulk modulus of K = 194(3) GPa. All the experimental data was compared to density functional theory calculations, which were observed to fit well with the experiments.