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 a 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 °C). The incorporation of W/Cr ions disrupts the long-range order of the crystal lattice, which induces significant distortion of the [Nb/Ti]O₆ octahedral and generates more stable domain structures, contributing to an enhanced piezoelectric response and high Curie temperature. Meanwhile, W⁶⁺ donor doping and the formation of $({\text{Cr}}_{\text{Ti}}^{{}^{\prime }}-{\mathrm{V}}_{\mathrm{O}}^{\cdot \cdot })$ defect dipoles synergistically reduced the concentration of oxygen vacancies, thereby achieving both a high resistivity (ρ = 7.3×10⁷ Ω·cm) and a low dielectric loss (tanδ = 0.057) under high temperature conditions (@500 °C). In addition, the d₃₃ of the 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 °C. All results indicate that 0.3NBN–0.7BTN–WC_0.04 ceramics can be good candidates for piezoelectric sensor applications in high-temperature harsh environments.