Crystal structure, ferroelectric and piezoelectric properties of epitaxial (1−x)(Bi0.5Na0.5)TiO3–x(Bi0.5K0.5)TiO3 films grown by hydrothermal method

Epitaxial (K,Na)NbO3 (KNN) thin films were deposited on (001)SrRuO3/Pt/ZrO2/Si substrates by RF magnetron sputtering and their post-annealing effects for the as-deposited epitaxial KNN thin films were investigated. By the annealing, the crystal system changed from tetragonal to orthorhombic system due to the release of the internal stress. Asymmetry of the polarization-electric field (P–E) hysteresis loops along the electric field were changed from positive to negative side by the annealing. It represents that stable spontaneous polarization P s was changed from upward to downward direction induced by increasing of A-site vacancies. The displacement-electric field (D–E) curves of the epitaxial KNN/Si unimorph cantilevers also showed asymmetric behaviors. Relatively high converse piezoelectric coefficient |e 31,f | = 6.4 C/m2 was obtained from the 5 h-annealed epitaxial KNN thin films.

Section: Introductionmentioning

confidence: 99%

Annealing effects on epitaxial (K,Na)NbO₃ thin films grown on Si substrates

Tanaka

Ogawa

Kweon

et al. 2022

“…Self-polarization behavior was also reported for Pb(Zr,Ti)O 3 and (Bi,Na)TiO 3 -(Bi,K)TiO 3 films prepared by hydrothermal synthesis, indicating that the self-polarization behavior is typical of hydrothermally synthesized films. [31][32][33][34][35] Self-polarization means that the polarization of the film is aligned to one direction without any poling treatment. To realize this situation, the external force that the polarization direction makes align one direction is essential during the film deposition process.…”

Section: Resultsmentioning

confidence: 99%

Thermal stability of self-polarization in a (K,Na)NbO₃ film prepared by the hydrothermal method

Tateyama

Ito

Shiraishi

et al. 2021

Self Cite

Herein, the systematic change in the self-polarization behavior against the post-heat treatment after film deposition was investigated to understand the origin of self-polarization in hydrothermally prepared (K x Na 1−x )NbO 3 films with x = 0.88 at 240 °C below the Curie temperature. The transverse piezoelectric constant, e 31,f , was evaluated by the cantilever method. The as-prepared films and heat-treated films at 300 °C had an almost perfectly self-polarized state and showed e 31,f of ∼−5.0 C m −2 without applying an electric field as a poling treatment. Also, the piezoelectric response shows good linearity with the asymmetric piezoelectric butterfly curves, showing imprint characteristics. The self-polarized states were maintained until the heat treatment above the Curie temperature. Moreover, the self-polarized film was successfully deposited on the post-heattreated film without the self-polarized state. This result suggests that the self-polarized state is generated regardless of the polarized state of the underlying layer by the hydrothermal synthesis in which deposition temperature is below the Curie temperature.

“…In an atomically homogeneous solid solution, the Bi-O covalent bond cannot extend with x > 0.4 and the resultant lattice is regarded as pseudo-cubic. 38,[74][75][76][77][78] Materials design that enables to develop a Bi-O covalent bond or a choice of end members such as (Bi, Na)TiO 3 [79][80][81][82][83] and/or (Bi, K)TiO 3 84,85) are necessary for further development of BiFeO 3 -based solid solution ferroelectric and piezoelectric ceramics.…”

Section: Discussionmentioning

confidence: 99%

Ferroelectric polarization of tetragonal BiFeO₃—an approach from DFT calculations for BiFeO₃–BaTiO₃ superlattices—

Noguchi

Matsuo

2022

Density functional theory calculations are conducted for tetragonal BiFeO3–BaTiO3 superlattices to investigate the influence of electronic structures on ferroelectric spontaneous polarization (Ps). When the number of the perovskite unit cell in one layer (N) is decreased below 10, the Ps starts to decrease from the volume-averaged one of 50.9 C/cm2 and eventually becomes half at N = 1. In the BiFeO3 cell (N = ∞) with a large Ps (73.3 C/cm2), a Bi-O covalent bond arising from a Bi_6p-O_2p orbital interaction is extended in an -O-Bi-O- network, and stereo-chemical lone-pair electrons of Bi are accommodated in the opposite direction of the c axis. In the superlattice with N = 1, the -O-Bi-O- bonding is interrupted by Ba and then the Bi-O bond becomes ionic. We show that the large Ps of the BiFeO3 cell originates from the Bi_6p-O_2p mixing superimposed on the stereo-chemical nature of lone-pair electrons of Bi.