Crystal structure of lutetium aluminate (LUAM), Lu4Al2O9.

Rayko Simura,Hisanori Yamane

doi:10.1107/s2056989020005757

Rayko Simura, Hisanori Yamane

Open Access

https://doi.org/10.1107/s2056989020005757

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Abstract

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) Å3, 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.

Highlights

In the Al2O3-Lu2O3 system, where Lu has the largest atomic number among the rare-earth elements (RE), the following three phases have been reported: Lu3Al5O12, LuAlO3, and Lu4Al2O9
Klimm (2010) employed differential thermal analysis (DTA) to investigate LuAlO3 melting behavior in a 5 N pure Ar flow and concluded that the congruent and incongruent melting of LuAlO3 depended on the atmospheric conditions
The author concluded that the phase diagram at around Lu:Al = 1:1 under an inert atmosphere, previously reported by Wu & Pelton (1992), is correct

Summary

Chemical context

In the Al2O3-Lu2O3 system, where Lu has the largest atomic number among the rare-earth elements (RE), the following three phases have been reported: Lu3Al5O12, LuAlO3, and Lu4Al2O9. Christensen & Hazell (1991) later determined the crystal structure of Y4Al2O9 using powder synchrotron X-ray and neutron diffraction. Yamane et al (1995a) reported that only a very small amount of Lu4Al2O9 can be obtained by reactions in air at 1673–2073 K, even though RE4Al2O9 (RE = Y, Sm–Yb) can be synthesized under the same conditions Following these reports, the present authors attempted to synthesize Lu4Al2O9 by heating a 2:1 molar ratio powder mixture of Lu2O3 and Al2O3 at 2073 K for 2 h in air, but the sample obtained was a mixture of LuAlO3 and Lu2O3 (see Fig. S1a in the supporting information). The method used to prepare the single crystals of Lu4Al2O9 used for the present diffraction study is described below

Structural commentary

Findings

Synthesis and crystallization