Electron Spin Resonances in Reduced BaTiO₃

Abstract

Electron spin resonances of reduced BaTiO₃ were observed in X band at 77°K and 55°K. The paramagnetic centers in the crystals reduced at temperatures between 650°C and 1000°C have three equivalent sites, each of which shows tetragonal symmetry. The g tensor is axial symmetric: g_⁄⁄=1,930 and g_⊥=1,911. Spin-lattice relaxation time is of the order of 10⁻⁶ s at 55°K. Resonance of impurity Pt³⁺ disappears in the crystals reduced at above 650°C. These facts indicate that the center observed is an F-center surrounded by two Ti⁴⁺ and four Ba²⁺ ions. Another kind of complex centers appear in the crystals reduced at 1100°C. The origin of these centers, however, has not been analyzed yet. With the crystals reduced at 1300°C, the two kinds of centers mentioned above completely vanish. This is due to purge of electron traps.