High-Frequency EPR Analysis of MnO2-Doped [Bi0.5Na0.5]TiO3-BaTiO3 Piezoelectric Ceramics – Manganese Oxidation States and Materials ‘Hardening’

High-frequency electron paramagnetic resonance (EPR) has been used to identify different manganese oxidation states in the 0.5 mol% MnO2-doped (100-x)Bi0.5Na0.5TiO3-xBaTiO(3) (BNT-xBT) solid solution with x = 6. The as-sintered and air-annealed samples show two distinct EPR resonances that were assigned to Mn2+- and Mn3+ -ions, respectively, incorporated at the Ti-site. The equilibrium between acceptor-type Mn "(Ti)- and Mn'(Ti)-states can be explained by the thermodynamic equilibration under air at the sintering temperature corresponding to [n] > [p], which yields an n-type Mn:BNT-6BT compound.