Growth of complex oxide single crystals with high melting point over 2200 °C using tungsten crucible

Complex oxide single crystals with melting points (MPs) above 2200 °C cannot be grown from the melt using iridium (Ir) or platinum (Pt) crucibles due to the MP limitations of these materials. To overcome this, we focused on the tungsten (W) crucibles, with MP above 3400 °C. The micro-pulling-down (µ-PD) method employing the W crucible and deoxygenated insulators enabled the growth of oxide single crystals with MP exceeding 2200 °C without any inclusions or deterioration of the W crucible. La₂Zr₂O₇ (MP: 2283 °C) and La₂Hf₂O₇ (MP: 2418 °C) single crystals with a pyrochlore structure were successfully grown using W crucibles, and they exhibited high transparency after annealing in air. Additionally, we achieved the growth of Lu₃TaO₇ (MP: 2380 °C) single crystals with a density of 9.68 g/cm³. Lu₃TaO₇ single crystal is a promising scintillator material for high-energy radiation detection due to its ultra-high density and potential for fast decay via Cherenkov light emission. The luminescence and scintillation properties of dopant ions can be clarified in single crystals with rare-earth (RE) ions. These results demonstrate that the advanced growth method is useful tool for the development and study of high-MP optical materials and scintillators.