As a typical Aurivillius-type compound, CaBi₄Ti₄O₁₅ (CBT) is considered a strong competitor among high-temperature piezoelectric materials, but it is difficult to achieve both high piezoelectric activity and a high Curie temperature for CBT. In this work, the method of double-ion co-substituting at different crystalline sites was used to modify the electrical properties of CBT. The Gd/Mn co-doped CBT ceramics with the chemical formula of Ca_1−xGd_xBi₄Ti₄O₁₅+0.2 wt% MnO₂ (CBT–100xGM, x = 0–0.11) were prepared via the conventional sintering process. The phase and valence band structures, chemical compositions and microstructures, dielectric and ferroelectric properties, electrical conduction behaviors, and electroelastic and piezoelectric properties of the ceramics were characterized. The doping concentration effects of Gd³⁺ were analyzed according to the composition-dependent structures and properties of CBT–100xGM. The donor substitution of Gd³⁺ for Ca²⁺ at the A-site reduced the tolerance factor of the perovskite-like structure and decreased the concentration of intrinsic oxygen vacancies. While Mn³⁺ tended to substitute for Ti⁴⁺ at the B-site, the extrinsic oxygen vacancies are limited near the defect center of Ti(Mn) because of the formation of ( ${\mathrm{V}}_{\mathrm{O}}^{\cdot \cdot }$‒Mn_Ti^')^• as defect dipoles. The thermal depoling behavior of the CBT–100xGM ceramics between 300 and 700 °C was explained by the thermodynamic characteristics of the defect dipoles. The optimized composition with x = 0.08 (CBT–8GM) had a high T_C ≈ 809 °C and a high piezoelectric coefficient (d₃₃) ≈ 23 pC/N, as well as a piezoelectric voltage constant (g₃₃) value of up to 21.5×10⁻³ (V·m)/N. Moreover, it can maintain a residual d₃₃ ≈ 80% after being annealed at 700 °C. This good anti-thermal depoling ability endows this material with great application potential in high-temperature piezoelectric devices with operating temperatures exceeding 500 °C. The synergistic enhancement in the piezoelectric activity and Curie temperature of CBT can be attributed mainly to the donor-substituting effect of Gd³⁺ at the A-site, as well as the decreased elastic compliance contributed by MnO₂ as the B-site dopant.

High-performance Pb(Zr_1−xTi_x)O₃ (PZT) piezoceramics are urgently desired by the market in view of their expanded operating temperature range, reduced property temperature dependence, and enhanced sensitivity and acoustic power. In this work, we reported a kind of low-cost and high-performance 0.06BiYbO₃–0.94Pb(Zr_0.48Ti_0.52)O₃ ternary piezoceramics; the modifying effects of La₂O₃ on this perovskite system were investigated in terms of the structures, electrical properties, and thermal depolarization behaviors of ceramics. The field-dependent dielectric and conduction properties indicated that there are close correlations among oxygen vacancies (V_O), conducting electrons, and intrinsic conduction process. The degradation in ferroelectric properties observed in those samples doped with more than 0.15 wt% of La₂O₃ indicated that the occupying mechanisms of La³⁺ changed from the donor substitution for Pb²⁺ to the isovalent substitution for Bi³⁺. The thermally depoling micromechanisms of ceramics were revealed from the thermodynamic processes of defect dipoles and intrinsic dipoles within ferroelectric domains. The sample doped with 0.15 wt% of La₂O₃ shows excellent electrical properties with T_C = 387 ℃, d₃₃ = 332 pC/N, TK_ε = 5.81×10⁻³ ℃⁻¹, P_r = 20.66 μC/cm², T_d = 356 ℃. The significantly enhanced electrical properties and thermal depolarization temperature benefited from the donor substitution of La³⁺, decreasing the oxygen vacancy concentration in the lattice and possibly optimizing the ferroelectric domain structure of ceramics.

In this work, different amount of Cr₂O₃ (x = 0–0.3 wt%) as dopant were doped into the Aurivillius-type compound Bi_2.8Gd_0.2TiNbO₉ (BGTN), such a kind of Gd/Cr co-doped Bi₃TiNbO₉ ceramics with improved electrical properties were synthesized by the convenient solid-state reaction route. The substitution of Cr³⁺ for Ti⁴⁺ at B-site induced the lattice distortion of pseduo-perovskite layer. Fewer Cr₂O₃ dopant (x < 0.2) resulted in the grain refinement of ceramics. After Cr₂O₃ was added into BGTN, T_C decreased to the vicinity of 908 ℃. Below T_C, the relaxed dielectric response resulted from charge carriers hopping induced another board dielectric permittivity peak, whose starting temperature shifts toward lower side gradually with increase of x. The values of E_a^con calculated from the Arrhenius relationship between conductivity and temperature indicated the intrinsic conduction at high temperature is dominated by the long-range migration of doubly ionized oxygen vacancies. Moderate Cr₂O₃ dopant (x = 0.1–0.25) are conducive to the enhancement of piezoelectric property and thermal stability. The sample with x = 0.2 achieved both a high T_C~903 ℃ and a high d₃₃~18 pC/N at the same time. Also, its d₃₃ can retain 80% of the initial value after the sample was annealed at 800 ℃ for 4 h.