Improvement of energy storage properties with the reduction of depolarization temperature in lead-free (1 – <i>x</i>)Na0.5Bi0.5TiO3-<i>x</i>AgTaO3 ceramics

Abstract

The effects of electric field and temperature on structural, dielectric, and ferroelectric properties of (1 – x)(Na0.50Bi0.50TiO3)-xAgTaO3 (x = 0, 0.03, 0.05, and 0.10) ceramics prepared via the modified sol-gel method were investigated. Rietveld refinement of synchrotron radiation x-ray diffraction data (SRPXRD) confirmed the rhombohedral (R3c) phase in all the unpoled samples. After poling, the samples remained in the rhombohedral phase for x ≤ 0.03, whereas for x ≥ 0.05, it showed a mixed rhombohedral and tetragonal (P4bm) phase. The anti-phase octahedral tilt angle was found to increase from 8.49° to 9.50° (for x = 0) and from 7.60° to 7.85° (for x = 0.10) with poling due to the long-range ordering phenomenon in the lattice system. The temperature-dependent dielectric study showed that the depolarization temperature decreases with increasing composition. Unpoled x = 0.10 composition exhibited the wide thermal stability dielectric constant in the temperature range 120-450 °C with 1795 ± 15% (tan δ &amp;lt; 0.041). Polarization versus electric field measurement revealed that at room temperature, the presence of anti-ferroelectric ordering increases the energy storage efficiency from 2.6% (for x = 0) to 48.2% (for x = 0.10). With increasing temperature, it increased from 48.2% (30 °C) to 85.5% (140 °C) for x = 0.10 composition. Improvement in the energy storage efficiency was correlated with structural changes probed by temperature dependent SRPXRD measurements; it confirmed the increase in antiferroelectric ordering with increasing temperature. Dielectric and ferroelectric results indicate the usefulness of this material system in the field of wide thermal stability dielectric constant and high-temperature energy storage applications.