Electric-Field-Induced Phase Transitions in Antiferroelectric PbZrO3 Thin Films
Abstract
In this work, an extensive investigation towards understanding and controlling the electric field induced phase transition in PbZrO3 was taken, focusing on optimizing the processing conditions to control the microstructure and enhance the functional response, including electromechanical response, dielectric tunability, and energy storage density. First, Nb and Mg co-doping in PbZrO3 thin films with thickness <200 nm were fabricated, concluding that the phase transition electric field can be controlled with the size of the dopants. Because of the volatility of Pb at high crystallization temperatures, a certain percentage of Pb overstoichiometry is always incorporated in the precursors during the processing of Pb-based perovskite materials. 20-70% Pb overstoichiometry was incorporated into the precursor sol gel solution to study the change of microstructure as well as functional response with increasing excess Pb. 70% excess Pb was found to be the optimal percentage to obtain films with no surface nanocrystals. PbZrO3 thin films of different orientations were also prepared by controlling crystallization environment as well as utilizing PbO seed layer. Phase transition electric field, electric field induced strain, Curie temperature, etc were all found to be highly dependent on the orientation. 001-oriented PbZrO3 films showed large strain of 1.14% and comparable energy storage density than other ferroelectric and piezoelectric thin films, which is suitable for high precision actuators and energy storage devices. While 042-oriented films showed the lowest phase transition electric field and high tunability of 92%, which is more appropriate for high tunability filters. This works show that high functional response, including large electromechanical response, high dielectric tunability, high energy storage density and efficiency, etc., can be obtained in PbZrO3 films via optimizing the Pb overstoichiometry in the precursor solution and locally compensating Pb loss through PbO coating. This work also reveals the anisotropic nature of AP → P phase transition in PbZrO3 via fabricating highly oriented films. The knowledge of the dependence of phase transition on the orientation and chemical doping is beneficial for fabricating PbZrO3-based antiferroelectric materials for use in MEMS devices, energy storage devices, as well as tunable capacitors.