Crystal Chemistry and Dielectric Properties in the Systems BaTiO3-UO2 and BaTiO3-BaUO3

Polycrystalline barium titanate fired in nitrogen at 1300° to 1400°C accommodates up to 3 mole % UO2 in solid solution; its structure is then cubic at room temperature. With BaUO3 additions the structure becomes disordered and quasi‐cubic. In air, about 1 mole % UO2 goes into solid solution in BaTiO3 but the structure remains tetragonal. Diffraction peaks of a new phase, possibly a ternary oxide of barium, uranium, and titanium, appear in patterns of specimens containing more than 2 mole % UO2. The dielectric constant of BaTiO3 ceramics fired in air, steam, or oxygen increases with up to about 0.5 mole % UO2 but declines rapidly above this level. The dielectric constant of BaUO3 is about two orders of magnitude lower than that of BaTiO3, and additions of BaUO3 invariably lower the dielectric constant of BaTiO3.