High performance Bi_0.5Na_0.5TiO₃-BiAlO₃-K_0.5Na_0.5NbO₃ lead-free pyroelectric ceramics for thermal detectors

Both high pyroelectric properties and good temperature stability of ferroelectric materials are desirable when used for applications in infrared thermal detectors. In this work, we report lead-free ternary 0.97(0.99Bi_0.5Na_0.5TiO₃-0.01BiAlO₃)-0.03K_0.5Na_0.5NbO₃ (BNT-BA-KNN) ceramics, which not only exhibits a large pyroelectric coefficient (p ∼ 3.7 × 10^-8 C cm^-2K^-1) and figures of merit (F_i, F_v, and F_d) but also shows excellent thermal stable properties. At room temperature, F_i, F_v, and F_d are determined as high as 1.32 × 10^-10 m/V, 2.89 × 10^-2 m²/C, and 1.15 × 10^-5Pa^-1/2 at 1 kHz and 1.32 × 10^-10 m/V, 2.70 × 10^-2 m²/C, and 1.09 × 10^-5Pa^-1/2 at 20 Hz, respectively. During the temperature range of RT to 85 °C, the achieved p, F_i, F_v, and F_d do not vary too much. The high depolarization temperature and the undispersed ferroelectric-ergodic relaxor phase transition with a sharp pyroelectric coefficient peak value of ∼400 × 10^-8 C cm^-2K^-1 are suggested to be responsible for this thermal stability, which ensures reliable actual operation. The results reveal the BNT-BA-KNN ceramics as promising lead-free candidates for infrared thermal detector applications.