Structure of new metastable cubic TbO2−x

A new structure of TbO2−x with the Ia3¯ space group has been solved using single crystal diffraction techniques. From the structure refinement, a significant deficiency is found on one of the two oxygen sites which results in the TbO1.68(6) composition. Two types of Tb atoms with different bond valence sums and thus with two oxidation states exist in the structure. The phase does not obey the stability rules formulated for other oxygen deficient RnO2n−2m phases with R=Ce, Pr and Tb. The phase was obtained at high temperatures and is unstable at room temperature.