Comparison of multi-valent manganese oxides (Mn4+, Mn3+, and Mn2+) doping in BiFeO3-BaTiO3 piezoelectric ceramics

Different manganese oxides-doping effects were compared in piezoceramic BiFeO3-BaTiO3 system. 0.67Bi(1.05)(Fe0.99Mn0.01x)O-3-0.33BaTiO(3) (valence state x = 4 +, 3 + , and 2 + ) ceramics were prepared via a solid-state reaction process followed by furnace-cooling (FC) or water-quenching (WQ) process. For the FC ceramics, the direct piezoelectric sensor coefficient (d(33)) was almost independent of valence state of doped Mn, while d(33) depended on the fraction of Fe3+/Fe2+ in WQ ceramics. The d(33) value was highest for the donor Mn4+-doped ceramic, among the FC ceramics, with 175 pC/N. However, acceptor-doping with Mn2+ prevented the transition of Fe ion valence state from 3+ to 2+ in the WQ ceramics, the Mn2+-doped WQ ceramic showed the largest d(33) of 313 pC/N and converse piezoelectric actuator coefficient, d(33)* of 352 pm/V, with high Curie phase transition temperature (482 degrees C).