High pressure structure studies of 6H-SrIrO3 and the octahedral tilting in 3C-SrIrO3 towards a post-perovskite

• Structures of 6H- and 3C-SrIrO3 were studied to pressures of 43 and 60 GPa, respectively.
• Both structures maintain the initial symmetry up to the highest pressures measured.
• 6H-SrIrO3 is initially more compressible than 3C-SrIrO3.
• Due to changes in the compression mechanism in 6H-SrIrO3 the 3C-SrIrO3 remains denser throughout.
• 3C-SrIrO3 show large octahedral tilting, strongly suggesting a post-perovskite transition is imminent.

The high pressure behaviors of the two perovskite structures (hexagonal 6H-SrIrO3 and orthorhombic 3C-SrIrO3) have been studied in diamond anvil cells to 43 and 60 GPa, respectively, using synchrotron powder X-ray diffraction. 6H-SrIrO3 was first synthesized at ambient pressure and subsequently transformed into 3C-SrIrO3 in a large volume press at 8.8 GPa and 1000 °C. Both polymorphs were found to retain the initial symmetry up to the highest pressures measured, but in the case of 6H-SrIrO3, two anomalies were identified: a change in the axial compressibilities at 24 GPa and a change in both the axial and volume compressibilities at 32 GPa. Fitting a 3rd order Birch-Murnaghan equation of state to the obtained P-V data yielded bulk moduli of K0=151.5(12) GPa (fitted range 0

The structure of 3C-SrIrO3 synthesized at high pressure has been studied in a diamond anvil cell and is found to maintain its orthorhombic structure up to 60 GPa but distorts drastically due to octahedral tilting, strongly suggesting that a post-perovskite transition is possible. The compression is compared to 6H-SrIrO3 synthesized at ambient pressure, which is initially found to be more compressible but undergoes changes in its compression mechanism and 3C remains denser throughout compression.Figure optionsDownload as PowerPoint slide