Crystal structure of lutetium aluminate (LUAM), Lu₄Al₂O₉

The crystal structure of the title compound containing lutetium, the last element in the lanthanide series, was determined using a single crystal prepared by heating a pressed pellet of a 2:1 molar ratio mixture of Lu₂O₃ and Al₂O₃ powders in an Ar atmosphere at 2173 K for 4 h. Lu₄Al₂O₉ is isostructural with Eu₄Al₂O₉ and composed of Al₂O₇ di-tetra-hedra and Lu-centered six- and sevenfold oxygen polyhedra. The unit-cell volume, 787.3 (3) ų, is the smallest among the volumes of the rare-earth (RE) aluminates, RE ₄Al₂O₉. The crystal studied was refined as a two-component pseudo-merohedric twin.