The synthesis and crystal structure of α-Ca3UO6

Single crystals of α-Ca₃UO₆ were grown from a UO₃CaCl₂CaO melt by the slow cooling method from 950°C. The crystal structure was determined by means of X-ray diffraction with R = 0.032 and R_w = 0.019. The structure of α-Ca₃UO₆ is of Mg₃TeO₆ type. α-Ca₃UO₆ is rhombohedral with a = 6.729 (1)Å, α = 90.30 (1)°, Z = 2, D_c = 4.955 g/cm³, D_m = 4.79 g/cm³, space group $\text{R}\text{3}$. Uranium and calcium atoms are six-coordinated. At 1200°C rhombohedral α-Ca₃UO₆ irreversibly transforms to monoclinic β-Ca₃UO₆.