Realization of the Giant Pyroelectric Response via Modulated Polar Structures

Abstract

Among pyroelectric materials, Bi_0.5 Na_0.5 TiO₃ (BNT)-based relaxors are particularly noteworthy due to their significant polarization fluctuation near the depolarization temperature (T_d ), resulting in a large pyroelectric response. What has been overlooked is the dynamic behavior of inherent polar structures, particularly the temperature-dependent evolution of polar nanoregions (PNRs), which significantly impacts the pyroelectric behavior. Herein, based on the large pyroelectric response origination (the ferroelectric-relaxor phase transition), the mixed nonergodic and ergodic relaxor (NR+ER) critical state is constructed, which is believed to trigger the easily fluctuating polarization state with excellent pyroelectric response. Composition engineering (with Li⁺ , Sr²⁺ , and Ta⁵⁺ ) strategically controls the relaxor process and modulates the dynamic behavior of inherent polar structures by the random field effect. The pyroelectric coefficient of more than 1441 µCm^-2 K^-1 at room temperature (RT), more than 9221 µCm^-2 K^-1 (RT), and ≈107911 µCm^-2 K^-1 (T_d ) are achieved in the Li⁺ -doped sample, the Sr²⁺ -doped sample, and the (Li⁺ +Ta⁵⁺ ) co-doped sample, respectively. This work earns the highest RT pyroelectric coefficient in BNT-based relaxors, which is suitable for pyroelectric applications. Furthermore, it provides a strategy for modulating the pyroelectric performance of BNT-based relaxors.

Keywords: Bi0.5Na0.5TiO3; electrocaloric effect; pyroelectric effect; relaxor ferroelectrics.