Relaxation behavior and energy storage of A-site substituted Sr 4− x Na 2− x La x Ta 0.6 Nb 9.4 O 30 ferroelectric ceramics

The tungsten bronze ceramics were prepared by solid-state reaction method to investigate the effect of La 3+ concentration on the microstructure, dielectric and ferroelectric properties of Sr 4 − x Na 2 − x La x Ta 0.6 Nb 9.4 O 30 (SNLTN: 0 ≤ x ≤ 0.4). X-ray diffraction results show that the tungsten bronze phase structure was a tetragonal phase in the P4bm space group at room temperature. The A-site structural vacancies increases as the structure transformed from “filled” to “unfilled” state. At the same time, the distortion of the BO 6 octahedral increases. The results of the temperature dependence of the dielectric constant indicate that adding La 3+ promotes the emergence of dipole-glass-like behavior and enhances dielectric relaxation. To better understand how polar clusters in Sr 4 − x Na 2 − x La x Ta 0.6 Nb 9.4 O 30 ceramics change with increasing x , the size and kinetic behavior of PNRs were calculated and analyzed using the Vogel-Fulcher relationship and macroscopic and phenomenological statistical model, which reveals that the thermal stability of the dielectric constant is inversely related to the size of PNRs in addition to the long-range ordering of the system is disrupted. Hence, it is critical for the energy storage performance to obtain small size and the high number of active PNRs and the weak coupling between PNRs and other polar clusters. Finally, an energy storage density of 2.06 J/cm 3 was received in Sr 3.8 Na 1.8 La 0.2 Ta 0.6 Nb 9.4 O 30 .