Single-crystal growth and crystal structure refinement of CuAlO2

Single crystals of the delafossite-type compound CuAlO₂ were grown from Al₂O₃Cu₂O melt by a slow-cooling method from 1200°C. Three types were found in as-grown crystals (single crystals, short-columnar twin crystals with concave angles, and laminar twin crystals). The twinning form is similar to the spinel-type twin. CuAlO₂ is rhombohedral, $\text{R}\text{3}\text{m, a = 2.8604(7), c = 16.953(5)}\text{A}\text{?}$, Z = 3, Dx = 5.12 g/cm³ and Dm = 5.06 g/cm³. The crystal structure of CuAlO₂ was analyzed by means of single-crystal X-ray diffraction with a conventional R value = 0.038. The value of the U₁₁ component of the thermal parameter of Cu⁺ was twice as large as U₃₃.