Electronic states of Mn ions in Ba0.97Sr0.03TiO3 single crystals

Abstract

The electronic states of Mn ions in barium titanate have been studied on Mn‐doped and Mn, Gd‐codoped Ba_0.97Sr_0.03TiO₃ single crystals, using ESR and optical absorption techniques. It was found from ESR measurements that Mn ions substitute at the B sites and exist as Mn²⁺ in reduced crystals and Gd‐doped crystals, and as Mn³⁺ in fully oxidized crystals. Optical measurements indicated that the energy levels of Mn²⁺ and Mn³⁺ are above and below the Fermi level, respectively. Moreover, resistivity measurements showed that the conductivities of the specimens are associated with the difference between their concentration of Gd and Mn ions. These results indicate that, when donors are increased by reduction or doping of Gd³⁺, Mn³⁺ ions trap the donor electrons to change into Mn²⁺.