Synergistically enhances piezoelectricity and resistivity of high temperature 0.3Na_0.5Bi_2.5Nb₂O₉–0.7Bi₃TiNbO₉ ceramics by (W,Cr) co-doping

0.3Na_0.5Bi_2.5Nb₂O₉-0.7Bi₃Ti_1-x(W_1/3Cr_2/3)_xNbO₉ (0.3NBN-0.7BTN-WC_x, x=0-0.06) high Curie temperature piezoceramics with bismuth layered structure were prepared by a solid-state reaction method. The optimized 0.3NBN-0.7BTN-WC_0.04 ceramics possess an enhanced piezoelectric constant (d₃₃=20.3 pC/N) with a very high Curie temperature (T_C=845.9 ^oC). The incorporation of W/Cr ions disrupts the long-range order of the crystal lattice, which induces significant distortion of [Nb/Ti]O₆ octahedral and generates more stable domain structures, contributing to enhanced piezoelectric response and high Curie temperature. Meanwhile, W⁶⁺ donor doping and the formation of  defect dipoles synergistically reduced the concentration of oxygen vacancies, thereby achieving both high resistivity (ρ=7.3×10⁷ Ω·cm) and low dielectric loss (tanδ=0.057) under high temperature condition (@500 ^oC). In addition, the d₃₃ of 0.3NBN-0.7BTN-WC_0.04 ceramics exhibits excellent thermal stability, retaining 93.1% of its initial value (d₃₃=18.9 pC/N) after annealing at 600 ^oC. All results indicate that 0.3NBN-0.7BTN-WC_0.04 ceramics can be a good candidate for piezoelectric sensor application in high temperature harsh environments.