Abstract
Dense Bi0.487Na0.427K0.06Ba0.026TiO3 (BNKBT) and Nb-doped Bi0.487Na0.427K0.06Ba0.026Ti0.98Nb0.02O3 (Nb-BNKBT) ceramics were prepared by the solid state reaction route. BNKBT is a non-ergodic relaxor and exhibits a piezoelectric response typical for a ferroelectric, whereas Nb-BNKBT is an ergodic relaxor and exhibits an electromechanical response typical for an incipient ferroelectric. The incorporation of 2 mol% of Nb into the BNKBT lattice is accompanied by an enhancement of the room-temperature unipolar field-induced strain from 0.19% to 0.43% at 75kV/cm. BNKBT shows a depolarisation temperature of ∼90°C, above which an electrostrictive response is observed, whereas Nb-BNKBT shows an electrostrictive response in the entire temperature range studied. At 40kV/cm, Nb-BNKBT exhibits a temperature stable electromechanical response in comparison with undoped BNKBT, but it worsens under higher electric fields. These results may motivate further investigations on the impact of minor doping and driving electric fields on the electromechanical response of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BaTiO3-based ceramics.
Highlights
Piezoelectric or electrostrictive actuators convert directly electrical energy into precisely controlled mechanical displacements
The typical microstructures of BNKBT and Nb-BNKBT ceramics fired at 1050 °C for 4 h are illustrated in Fig. 3a and b, respectively
A non-ergodic relaxor with the nominal composition K0.06Bi0.487Na0.427Ba0.026TiO3 was transformed into an ergodic relaxor by chemical substitution of Ti by 2 mol% Nb
Summary
Piezoelectric or electrostrictive actuators convert directly electrical energy into precisely controlled mechanical displacements. Within some technological areas such as aerospace and automotive, temperature stability of the electromechanical response is a stringent pre-requisite These actuators are invariably fabricated from Pb(Zr,Ti)O3 (PZT)-based ceramics because of their large field-induced strain combined with large electromechanical coupling coefficients for compositions lying at morphotropic phase boundary between rhombohedral and tetragonal symmetries. A giant strain of ∼0.87% under an applied electric field of 40 kV/cm was measured by Teranishi et al [4] in Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BaTiO3 (BNT-BKTBT) tetragonal single crystals, along the [100] direction. This value is six times larger than that exhibit by PZT, which led several researchers to investigate the electromechanical response of ceramics in this ternary system. Nb doping enhanced the thermal stability of the electromechanical properties, leading to materials with potential application in actuators operating at least up to 100 °C
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