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

We report on the synthesis and high pressure behavior of three polymorphs of SrGeO3. At ambient pressure, SrGeO3 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 K0 = 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 K0 = 194(3) GPa. All the experimental data was compared to density functional theory calculations, which were observed to fit well with the experiments.