Phase Transitions in the System BaTiO3-KnbO3

Abstract

Solid solution formation in the system BaTiO3—KnbO3 was established by X-ray diffraction and dielectric measurements. Solid solutions with cubic symmetry were observed in the composition range from 4 to 90 mole % KnbO3 at room temperature. The lattice parameter for the BaTiO3 solid solutions increased with increasing KNbO3; that for the KnbO3 solid solutions decreased with the addition of BaTiO3. A distinct discontinuity in lattice parameter was observed at the composition containing about 65 mole % BaTiO3. Dielectric measurements were made from-195° to 400°C. The cubic-tetragonal transition temperature of BaTiO3 was rapidly lowered with increasing addition of KNbO3, whereas the two lower phase transition temperatures were raised. All three phase transitions of KnbO3 were rapidly lowered with increasing addition of BaTiO3. The observed phase transitions, lattice parameters, and electron probe data suggest a complex region in the subsolidus which extends from 35 to about 75 mole % KNbO3.