Enhanced energy storage properties in A-site substituted Na0.5Bi0.5TiO3 ceramics

Detailed temperature-dependent structural, dielectric, piezo/ferroelectric, and energy storage properties were explored for the poled (Na0.5-xKxBi0.5-xLax)TiO3 (0 <= x <= 0.12) ceramics fabricated via a modified solgel method. Structural analysis of synchrotron source powder XRD data revealed the rhombohedral (R3c) phase for poled x <= 0.03 compositions. Whereas for x >= 0.06 samples confirmed structural transition, a mix of rhombohedral and tetragonal (P4bm) phase exists at room temperature. As a function of composition, a rhombohedral phase is found to be suppressed and the tetragonal phase promoted. Dielectric measurements corroborate that at room temperature; dielectric constant was increased with substitution. High-temperature dielectric measurement confirmed the reduction in phase transition temperatures and an increase in the diffuseness of dielectric anomalies with increasing content of K/La. Piezo/ferroelectric measurements revealed that x = 0.03 composition exhibits excellent piezo/ferroelectric properties (piezoelectric coefficient, d(33) similar to 115 pC/N, remnant polarization, 2P(r) similar to 56 mC/cm(2), and coercive field, 2E(c) similar to 100 kV/cm) at room temperature. Antiferroelectric ordering improved the energy storage density and efficiency at room temperature (similar to 0.05 J/cm(3), similar to 2.6% (for x = 0) to similar to 0.74 J/cm(3), similar to 87% (for x = 0.12)) and elevated temperature. For x = 0.06 sample, excellent energy storage density and efficiency similar to 1.10 J/cm(3) and similar to 70% respectively, are obtained at 120 degrees C. Superior energy storage efficiency showed by x = 0.12 (degrees 87-degrees 93%, in the temperature range 30-140 degrees C) with almost thermally stable energy storage density (from similar to 0.74 J/cm(3) to similar to 0.71 J/cm(3)). These drastic improvements in properties were explained in terms of structural changes as a function of composition and temperature. Observed properties suggest that substituted materials are promising candidates for piezoelectric (for x = 0.03) and energy storage (for x = 0.06) applications. (c) 2019 Elsevier B.V. All rights reserved.