Anomalous Phase Diagram of Ferroelectric(Ba,Ca)TiO3Single Crystals with Giant Electromechanical Response

Abstract

We report the anomalous phase evolution in ferroelectric single crystals Ba1-xCaxTiO3 (0.02<x<0.34), and demonstrate the significant effects of quantum fluctuation on the ferroelectric phase transition. In addition, large electromechanical responses in this class of crystals are also demonstrated. Our results indicate that an effective approach to control the ferroelectricity of perovskite oxide can be realized not only by the covalency between A site atom and oxygen but also by the substitution of A site with small ions with off-centering nature. Theoretical calculations support the idea that the off-center displacements of the smaller Ca ions in the Ba-site play an important role in the exotic natures of Ba1-xCaxTiO3.

Enhanced dielectric and ferroelectric characteristics in Ca-modified BaTiO3 ceramics

“…Fu firstly described this phase diagram in Ba 1−x Ca x TiO 3 single crystal, and suggested that the displacement of Ca stabilized the total energy of the unit cell. 10 The suppressed phase transitions due to Ca-substitution, especially for x ≥ 0.23, has also been interpreted by the soft-mode theory, which suggested that the off-centering nature of Ca could suppress the hopping of Ti ions and then reduce damping of the soft-mode. 18 Recently, Levin et al revealed the local structure origins of this phenomenon: both ferroelectric Ca displacements and their amplification of the Ti off-centering.…”

“…The previous work of first principle calculation indicated that Ca 2+ ions shifted to the off-centering positions due to its smaller ionic radius (1.34Å) than that of Ba (1.61Å), 15 leading to a local polarization in the A-site of the perovskite structure. 10 Levin's refinement results suggested that Ca had its own additional displacement as well as influenced the Ti displacement. 11 Our results reinforce these suggestions and evaluate the polarization in details.…”

“…[7][8][9] On the other hand, the effects of Ca-substitution in BaTiO 3 are quite unique, and the increasing interests have been received recently. 10,11 Ca-substitution could intriguingly sustain the Curie temperature while other alkaline metals indicate the severe size effects. Fu et al described the sustainable Curie temperature and the broadened tetragonal phase in Ba 1−x Ca x TiO 3 system, and suggested the additional displacement of Ca.…”

“…Fu et al described the sustainable Curie temperature and the broadened tetragonal phase in Ba 1−x Ca x TiO 3 system, and suggested the additional displacement of Ca. 10 Levin et al ascribed this phenomenon to both the displacements of Ca and their influence on Ti off-centering using Monte Carlo refinements of atomic positions by fitting of experimental data. 11 They revealed that Ca has its own ferroelectric displacement as a Author to whom correspondence should be addressed.…”

Simultaneous achievement of high dielectric constant and low temperature dependence of capacitance in (111)-oriented BaTiO3-Bi(Mg0.5Ti0.5)O3-BiFeO3 solid solution thin films

“…[6][7][8] These outstanding dielectric properties are due to the proximity of the Curie temperature (T c ) to the room temperature at around 100 • C. However, the dielectric properties of BaTiO 3 -based materials degrade dramatically at higher temperatures above 200 • C, because these properties obey the Curie-Weiss law in the paraelectric phase. 8,9 In a previous work, we proposed thin films of bismuth-layered perovskite dielectrics, such as CaBi 4 Ti 4 O 15 with its c-axis orientation, as candidate materials for high-temperature capacitor applications.…”