(Bi_1/2K_1/2)TiO₃ lead-free ferroelectric ceramics: processing, properties, and compositional modifications

Abstract

Bismuth potassium titanate (Bi 1/2 K 1/2 )TiO 3 with an A-site complex perovskite structure is regarded as a promising lead-free ferroelectric/piezoelectric material. Studies on the fundamental properties of (Bi 1/2 K 1/2 )TiO 3 have, however, been faced with difficulties in fabricating dense and phase-pure (i.e., "high-quality") bulk ceramics caused by its low melting point and the volatility of Bi and K. This paper reviews our findings on the fabrication process and fundamental properties of such high-quality (Bi 1/2 K 1/2 )TiO 3 ceramics. After a brief survey on the crystal structure and physical/chemical stability of (Bi 1/2 K 1/2 )TiO 3 , our fabrication process of (Bi 1/2 K 1/2 )TiO 3 ceramics utilizing the hydrothermal synthesis method is described. Then, the phase transition behavior of (Bi 1/2 K 1/2 )TiO 3 is discussed based on the electrical and electromechanical responses of the high-quality ceramic samples. The last part of this paper presents two examples of compositional modifications of (Bi 1/2 K 1/2 )TiO 3 ceramics aiming at developing dielectric and piezoelectric materials for use in capacitors and actuators.

Influence of temperature-induced A-site cation redistribution on the functional properties of A-site complex polar perovskite K1/2Bi1/2TiO3

“…23 The relaxation observed above the T F-R in the frequency-dependent dielectric response of KBT is often attributed to random fields 28,29 created by the presence of the disordered A-site Bi 3+ and K + cations. 12,30 Local structural analysis using total scattering and density functional theory calculations reported that long-range ordering of A-site cations in KBT is unfavorable. 11,12 It is important to note, unlike displacive ferroelectrics where B-site cation off-centering is the major contributor to the polarization, the increased tetragonal distortion associated with the A-site cation ordering is critical for the polarization in KBT.…”

Preparation of {100}-oriented (1−x)(Bi,K)TiO3−xCaTiO3 solid-solution epitaxial films by the hydrothermal method and their ferroelectric and piezoelectric properties

“…16,17) Therefore, (Bi,K)TiO 3 is expected to be used as one of the essential ferroelectric materials, similar to PbTiO 3 and BaTiO 3 . 18,19) Although the discovery of (Bi,K)TiO 3 dates back to the 1950s, the preparation of high-quality (Bi,K)TiO 3 film has been challenging mainly due to the preparation difficulties resulting from the high volatility of potassium and bismuth. 20,21) In 2022, our group reported on the growth of polar-axis-oriented epitaxial (Bi,K)TiO 3 film on (100) c SrRuO 3 //(100)SrTiO 3 substrate at a low deposition temperature of 240 °C by the hydrothermal method.…”

High-quality ferroelectric Bi0.5K0.5TiO3‒BiFeO3 solid-solution single crystals grown under high-pressure oxygen atmosphere

“…[1][2][3] However, the toxicity of Pb demands the replacement of Pb-based ferroelectrics with Pb-free ones. Researchers have developed various Bi-based ferroelectrics such as (Bi 0.5 Na 0.5 )TiO 3 (BNT), [4][5][6] (Bi 0.5 K 0.5 )TiO 3 (BKT), [7][8][9] BiFeO 3 (BFO), 10,11) and their solid solutions [12][13][14][15][16][17][18] as alternatives to PZT, and they are possible candidates because of their large P s and high T C .…”

“…[31][32][33][34][35] BKT is tetragonal (P4mm) perovskite ferroelectrics with a large tetragonality (c/a = 1.02) and relaxor-like broad dielectric peak with a high dielectric maximum temperature of approximately 380 °C. 7,36) In our previous study, we found that xBKT-(1 −x)BFO ceramics have an MPB between R3c and P4mm in 0.40 < x < 0.43, and 0.40BKT-0.60BFO ceramics exhibit a large remanent polarization (P r ) of 52 μC cm −2 , an excellent effective piezoelectric strain constant d 33 * of 130 pm V −1 , and a high T d of approximately 300 °C owing to its high T C of 430 °C. 26) Whereas the attractive T d of the BKT-BFO system motivates researchers to ceramics studies, single-crystal studies have not been performed so far in spite of its advantage to investigate the detailed electrical properties and crystal structures.…”