Sintering condition-dependent electromechanical behavior of the lead-free piezoelectric Bi1/2K1/2TiO3

Abstract

Sintering conditions govern the optimized functional properties of ceramics. However, solid-state processing of Bi1/2K1/2TiO3 (BKT), an important end member for lead-free piezoelectric solid solutions suitable for higher temperature (≤ 300 °C) transducer applications, is challenging due to the low melting temperature (≈1070 °C). In this work, the sintering temperature (1030 °C, 1050 °C, and 1060 °C) and dwell time (10 h, 20 h, and 40 h)-dependent functional properties of solid-state processed BKT were investigated, where the sintering condition-dependent dielectric and electromechanical properties were correlated with the variations in crystal structure and microstructure. Although X-ray diffraction data revealed a single-phase tetragonal structure of BKT at room temperature for all sintering conditions, significant changes in both the tetragonal distortion and spontaneous relaxor-ferroelectric transition were observed, which were directly related to the optimized functional properties. In addition, Rayleigh behavior of the piezoelectric coefficient was characterized between −150 °C and 400 °C, demonstrating that the electromechanical response is dominated by the intrinsic contribution, which can be explained by large tetragonal distortion and associated suppression of non-180° domain wall motion.

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

“…The dielectric response of the sample cooled with 5 K min −1 rate (NC 900 ) (Fig. 2a) matches well with that of previously reported as-processed KBT ceramics, 27,40 indicating 5 K min −1 cooling from 900 °C does not signicantly inuence the dielectric response of KBT. The NC 900 sample exhibits a relatively high maximum dielectric permittivity of 4500 at the temperature of maximum permittivity, T m of 378 °C at 1 MHz, where T m varies with measurement frequency.…”

“…Therefore, the origin of such an increase is not known; however, a relative change in structure distortion and extrinsic domain wall contributions could play a role here. Our previous work 40 on the stress-amplitude-dependent Rayleigh analysis of KBT revealed that the temperature-dependent relative change of intrinsic and extrinsic contributions to the overall piezoelectric coefficient can differ depending on the variation in tetragonal distortion of the as-processed sample. Nevertheless, further investigation of the variation in tetragonal distortion by in situ temperature-dependent diffraction measurement will be required to understand this.…”

“…As previously noted, the sharpness of the dielectric anomaly at the T F-R and thermal hysteresis indicates a RE-FE state change, whereas the absence of dielectric anomaly and thermal hysteresis suggests the stabilization of the RE state at room temperature. 40 The Q 900 sample (Fig. 4c) displays a higher permittivity value at the T m and a sharp transition at the T F-R , indicating the FE-RE state change similar to the NC 900 sample.…”

“…The mixture obtained after removing the ethanol in a rotary evaporator was calcined using a two-step calcination procedure at 750 °C for 5 h and 900 °C for 3 h to ensure phase pure KBT. 40 Calcinated powders were uniaxially pressed at ≈60 MPa to form pellets with a diameter of 10.2 mm and then cold isostatically pressed at 180 MPa. The green bodies were sintered in a closed alumina crucible at 1060 °C for 40 h. 40 Sintered KBT ceramics were subsequently ground for electromechanical characterization by a surface grinder to a final thickness of 0.5 mm.…”

“…40 Calcinated powders were uniaxially pressed at ≈60 MPa to form pellets with a diameter of 10.2 mm and then cold isostatically pressed at 180 MPa. The green bodies were sintered in a closed alumina crucible at 1060 °C for 40 h. 40 Sintered KBT ceramics were subsequently ground for electromechanical characterization by a surface grinder to a final thickness of 0.5 mm. It is important to note before the annealing experiment, the as-sintered samples were treated at 600 °C for 1 h followed by cooling to room temperature to remove the internal stress due to the machining and to establish identical sample history.…”