Growth of large (1 mm) MgSiO₃ perovskite single crystals: A thermal gradient method at ultrahigh pressure

Large single crystals of MgSiO₃ perovskite were successfully synthesized by a thermal gradient method at 24 GPa and 1500 °C. This was achieved by an improvement of high-pressure synthesis technique that allowed us to grow single crystals under such ultrahigh-pressure conditions in relatively large volumes (e.g., 10 mm³). Since crystal growth is hindered by neighboring crystals, the nucleation density was suppressed by reducing the thermal gradient to 20 °C/mm, permitting an increase in free space for large crystal growth. KHCO₃-Mg(OH)₂ solvent can be used to grow perovskite crystals. However, the carbonate solvent produces melt inclusions. Silicate sources with MgSiO₃ composition produce stishovite inclusions, which in turn cause splitting of perovskite crystals. The formation of these inclusions is avoided by using H₂O as a solvent and 85MgSiO₃-15Mg₂SiO₄ as a silicate source. The H₂O also allows homogeneous crystal growth, probably because of its low viscosity and high silicate solubility. High-quality single crystals larger than 1 mm were successfully synthesized through these technical developments.