Temperature dependent, large electromechanical strain in Nd-doped BiFeO3-BaTiO3 lead-free ceramics

Lead-free piezoceramics with the composition 0.7(Bi1-xNdx)FeO3-0.3BaTiO3+0.1wt% MnO2 (BNxF-BT) were prepared using a conventional solid state route. X-ray diffraction and temperature dependent permittivity measurements indicated a transition from a composition lying at a morphotropic phase boundary (MPB) to a pseudocubic phase as a function of Nd concentration. The highest maximum strain (S max ∼0.2% at 60kV/cm) and effective piezoelectric coefficient (d 33*=333 pm/V) were obtained at room temperature for the composition BN0.02F-BT. The decrease in remanent polarization (P r) and Berlincourt d 33 with increase in Nd concentration can be attributed to the coexistence of ferroelectric and relaxor phases. In-situ polarisation and strain measurements revealed an increase in Pr and d 33* with temperature and a reduction in the coercive field E C. Presumably this behavior is due to a combination of thermally activated domain wall motion and lowering of the activation energy for a field induced relaxor-ferroelectric transition, as the Curie maximum is approached