Abstract
A large piezoelectric response in ferroelectric ceramics is typically associated with extrinsic contributions from ferroelectric domain structures. However, such domain structures cannot be expected in systems with pseudo-cubic symmetry. In this study, we determine the mechanism of significant piezoelectricity and ferroelectricity in 0.3BaTiO3–0.1Bi(Mg1/2Ti1/2)O3–0.6BiFeO3 ceramic with a perovskite-type pseudo-cubic symmetry. Synchrotron radiation X-ray diffraction reveals that the Bi ions in this ceramic essentially prefer to be off-centered at six sites by approximately 0.4 Å, in the cubic <100> directions. A phase transition occurs at TC ~725 K. However, the crystal seems to present a cubic symmetry even at room temperature. The large piezoelectric response is caused by the combinational partial ordering of the off-centered Bi ions, adapted to any direction of the applied electric field to the ceramic grains. The proposed mechanism for the emergence of a high polarization in the above system will enable designing novel Pb-free ceramics by controlling the fluctuated and off-centered ions under an applied electric field.
Highlights
A large piezoelectric response in ferroelectric ceramics is typically associated with extrinsic contributions from ferroelectric domain structures
The unexpectedly large piezoelectric strain electrically observed in strain–electric-field (S–E) curves, and the significant ferroelectricity presented in polarization–electric field (P–E) hysteresis loops cannot be explained by the crystal symmetry
It was reported that the high piezoelectric response exhibited in BNT–BT single crystal with pseudocubic symmetry is due to improper ferroelectric distortion caused by in-phase or antiphase oxygen octahedral tilting[21]
Summary
A large piezoelectric response in ferroelectric ceramics is typically associated with extrinsic contributions from ferroelectric domain structures. The unexpectedly large piezoelectric strain electrically observed in strain–electric-field (S–E) curves, and the significant ferroelectricity presented in polarization–electric field (P–E) hysteresis loops cannot be explained by the crystal symmetry. These unforeseen electric responses are unique to BT–BMT–BF ceramics, but have been reported for other Bibased piezoelectric systems possessing a pseudocubic symmetry[15,16,17]. Further studies are needed to reveal that the Bi displacement and the local distortion are directly related to the large electric responses Another probable explanation for the large responses in cubic systems could be an electric-field-induced phase transition[24,25,26]
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