Structural, electrical, and strain properties of stoichiometric 1−x−y(Bi0.5Na0.5)TiO3−x(Bi0.5K0.5TiO3)−y(Na0.5K0.5)NbO3 solid solutions

Results on two series of lead-free piezoelectric solid solutions of 1−x−y(Bi0.5Na0.5)TiO3−x(Bi0.5K0.5TiO3)−y(Na0.5K0.5)NbO3 (BNT-BKT-KNN) ceramics, synthesized in the vicinity of ferroelectric rhombohedral (x=0.17) and ferroelectric tetragonal (x=0.20) phase boundary of 1−x(BNT)–xBKT are presented. Orthorhombic KNN in stoichiometric proportion as third component with 0.0≤y≤0.06 is added to prepare these two series (i) with x=0.17 and (ii) with x=0.20. Addition of KNN up to a critical y is observed to improve tetragonality in both series and solid solubility of KNN was verified at least up to y=0.1 in this system. Depolarization temperature Td of these stoichiometric BNT-BKT-KNN series were found to be considerably lower than that of their parent BNT-BKT compositions. As a result of this, coexistence of polar and nonpolar phases for compositions at morphotropic phase boundary (MPB) were indicated at room temperature, resulting in pinched polarization versus electric field (P-E) loops and large strain (strain of ∼0.80% was observed for y=0.01 sample in ×20 series and strain of 0.50% was seen for y=0.04 sample in ×17 series) The MPB of ×17 and ×20 series found to be at y=0.04 and y=0.01, respectively.