title: Self-Poling of BiFeO3 Thick Films.
abstract: Bismuth ferrite (BiFeO3) is difficult to pole because of the combination of its high coercive field and high electrical conductivity. This problem is particularly pronounced in thick films. The poling, however, must be performed to achieve a large macroscopic piezoelectric response. This study presents evidence of a prominent and reproducible self-poling effect in few-tens-of-micrometer-thick BiFeO3 films. Direct and converse piezoelectric measurements confirmed that the as-sintered BiFeO3 thick films yield d33 values of up to ∼20 pC/N. It was observed that a significant self-poling effect only appears in cases when the films are heated and cooled through the ferroelectric-paraelectric phase transition (Curie temperature TC ∼ 820 °C). These self-poled films exhibit a microstructure with randomly oriented columnar grains. The presence of a compressive strain gradient across the film thickness cooled from above the TC was experimentally confirmed and is suggested to be responsible for the self-poling effect. Finally, the macroscopic d33 response of the self-poled BiFeO3 film was characterized as a function of the driving-field frequency and amplitude.
authors.affiliation: Electronic Ceramics Department, Jozef Stefan Institute , Jamova Cesta, 39, 1000 Ljubljana, Slovenia.|Jozef Stefan International Postgraduate School , Jamova Cesta, 39, 1000 Ljubljana, Slovenia.
authors.forename: Evgeniya
authors.initials: E
authors.lastname: Khomyakova
authors.affiliation: Electronic Ceramics Department, Jozef Stefan Institute , Jamova Cesta, 39, 1000 Ljubljana, Slovenia.
authors.forename: Matej
authors.initials: M
authors.lastname: Sadl
authors.affiliation: Electronic Ceramics Department, Jozef Stefan Institute , Jamova Cesta, 39, 1000 Ljubljana, Slovenia.
authors.forename: Hana
authors.initials: H
authors.lastname: Ursic
authors.affiliation: School of Materials Science and Engineering, University of New South Wales , Sydney, New South Wales 2052, Australia.
authors.forename: John
authors.initials: J
authors.lastname: Daniels
authors.affiliation: Electronic Ceramics Department, Jozef Stefan Institute , Jamova Cesta, 39, 1000 Ljubljana, Slovenia.|Jozef Stefan International Postgraduate School , Jamova Cesta, 39, 1000 Ljubljana, Slovenia.
authors.forename: Barbara
authors.initials: B
authors.lastname: Malic
authors.affiliation: Electronic Ceramics Department, Jozef Stefan Institute , Jamova Cesta, 39, 1000 Ljubljana, Slovenia.|Jozef Stefan International Postgraduate School , Jamova Cesta, 39, 1000 Ljubljana, Slovenia.
authors.forename: Andreja
authors.initials: A
authors.lastname: Bencan
authors.affiliation: Ceramics Laboratory, Swiss Federal Institute of Technology in Lausanne-EPFL , 1015 Lausanne, Switzerland.
authors.forename: Dragan
authors.initials: D
authors.lastname: Damjanovic
authors.affiliation: Electronic Ceramics Department, Jozef Stefan Institute , Jamova Cesta, 39, 1000 Ljubljana, Slovenia.|Jozef Stefan International Postgraduate School , Jamova Cesta, 39, 1000 Ljubljana, Slovenia.
authors.forename: Tadej
authors.initials: T
authors.lastname: Rojac
keywords: bismuth ferrite; microstructure; self-poling; strain gradient; thick films