Strain Behaviors of Manganese-Doped (Bi0.5Na0.5)TiO3-BaTiO3-(Bi0.5K0.5)TiO3 Lead-Free Ferroelectric Ceramics

Abstract

The strain hystereses of lead-free a(Bi0.5Na0.5)TiO3-bBaTiO3-c(Bi0.5K0.5)TiO3 (abbrev. as BNBK 100a/100b/100c) ferroelectric compositions inside and outside the morphotropic phase boundary (MPB) are investigated. It is found that BNBK 85.4/2.6/12, a composition well within the MPB, possesses notable actuating properties such as an induced electrostrain of about 0.14% and an apparent d33 of 295 pCN−1. BNBK 85.4/2.6/12 is further doped with various amounts of manganese (Mn) to improve its sinterability and ferroelectric characteristics. Intricate hysteresis behaviors are observed upon Mn doping. The total induced electrostrain of BNBK 85.4/2.6/12 in the 33-directon decreases dramatically from 0.14 to 0.05% when 0.2 mol% of Mn is introduced into the composition. It then recovers sharply as the Mn doping amount is increased progressively to 0.5 and then to 1.0 mol%. However, when the doping amount is further increased above 1.0 mol%, a significant decrease in electrostrain is observed again. The hysteresis data indicate that an electrostrain above 0.1% can be maintained when the Mn doping amount is in between 0.5–1.5 mol%. Once outside this doping range, the induced electrostrain is considerably smaller. By examining the evolution of crystalline phase composition with Mn doping, the mole content of rhombohedral phase is shown to be a critical factor in deciding the straining behaviors of the Mn-doped BNBK 85.4/2.6/12 ceramics. To each increasing step in Mn doping level, there is a marked similarity in the evolutions of the induced electrostrain and rhombohedral phase content.