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

Abstract

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 sol-gel 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, d33 ∼ 115 pC/N, remnant polarization, 2Pr ∼ 56 μC/cm2, and coercive field, 2Ec ∼ 100 kV/cm) at room temperature. Antiferroelectric ordering improved the energy storage density and efficiency at room temperature (∼0.05 J/cm3, ∼2.6% (for x = 0) to ∼ 0.74 J/cm3, ∼87% (for x = 0.12)) and elevated temperature. For x = 0.06 sample, excellent energy storage density and efficiency ∼1.10 J/cm3 and ∼70% respectively, are obtained at 120 °C. Superior energy storage efficiency showed by x = 0.12 (∼87–∼93%, in the temperature range 30–140 °C) with almost thermally stable energy storage density (from ∼0.74 J/cm3 to ∼ 0.71 J/cm3). 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.