Large Electromechanical Response in Lead‐Free La‐Doped BNKT–BST Piezoelectric Ceramics

• DOI: 10.1111/jace.12952
• Publication Date: 2014-04-30T13:21:55Z
• Authors: Amir Ullah; Aman Ullah; Ill Won Kim; Dae Su Lee; Soon Jong Jeong; Chang Won Ahn
• Keywords: 02 engineering and technology; 0210 nano-technology

Piezoceramics 0.99[(Bi0.5Na0.4K0.1)1−xLaxTiO3]−0.01[Ba0.7Sr0.3TiO3] (BNKT–BST–Lax, x = 0–0.030) were synthesized using a conventional solid‐state reaction method. X‐ray diffraction revealed a phase transition from a tetragonal to cubic phase at x ≥ 0.005. The maximum dielectric constant as well as the depolarization temperature (Td) decreased with increasing La content. La addition interrupted the polarization and strain hysteresis loops and demonstrates that the ferroelectric order of the BNKT–BST ceramics lead to a reduction in the remnant polarization and coercive field. However, the destabilization of the ferroelectric order is accompanied by a significant increase in the unipolar strain which is highest at x = 0.020 with a value of ~0.39% and corresponding normalized strain, d*33 (= Smax/Emax) of 650 pm/V. It was observed that the unipolar strain of x = 0.020 is very temperature insensitive up to 125°C, even at 125°C the d*33 is as high as ~431 pm/V. Moreover, an electric‐field‐dependent XRD was conducted to identify the main source of the high strain and a recoverable transformation from cubic to a rhombohedral–tetragonal mixed phase was observed. The recoverable field‐induced phase transformation is suggested to be the main cause for the obtained large strain at x = 0.020 in the BNKT–BST–Lax ceramics.