Novel polar oxides with exceptional pyroelectric performance: doping-induced polar transition in Ba6Pb3.2(PO4)6Cl2

Abstract

Among existing pyroelectric materials, inorganic polar oxides exhibit large pyroelectric coefficients. However, their pyroelectric performance is severely limited by the high dielectric constants due to the inverse relationship between pyroelectric figures of merit (FOMs) and dielectric constants. On the other hand, organic pyroelectric materials, while having lower dielectric constants and losses, suffer from poor stability, which greatly restricts their application. Regarding the above issues, we present a novel class of polar oxides, Ba₆Pb_3.2(PO₄)₆Cl₂ (BPPC) and Ba₆(Bi_0.5Na_0.5)₄(PO₄)₆Cl₂ (BBNPC), derived from a previously unreported transformation of non-polar apatite structures. These materials exhibit exceptionally low dielectric constants (∼10) and losses (∼0.002), (room-temperature, 10 kHz frequency) combined with high stability. Notably, BPPC demonstrates outstanding pyroelectric performance, with a pyroelectric coefficient of 110 μC m⁻² K⁻¹. The pyroelectric figures of merit (FOMs) for BPPC (room-temperature, 10 kHz frequency, F_v = 0.7 m² C⁻¹, F_D = 17.0 × 10⁻⁵ Pa^1/2, F_E = 5.12 × 10⁻¹¹ m³ J⁻¹) surpass those of most existing inorganic pyroelectrics and approach the performance of leading organic materials. This pioneering doping strategy, leveraging size differentiated atomic substitution to induce spontaneous polarization, opens new avenues for designing high-performance polar oxides with potential applications in ferroelectric, piezoelectric, and photonic technologies. Our findings significantly expand the scope of polar functional materials beyond traditional perovskite-type oxides.