Enhanced piezoelectric properties and electrical resistivity of Na⁺/Nd³⁺ co-doped Ca_1−x(Na_1/2Nd_1/2)_xBi₄Ti₄O₁₅ ceramics for high-temperature applications

In bismuth layered structure ferroelectrics (BLSFs), relatively low piezoelectric coefficients (d₃₃) and DC electrical resistivity (ρ_dc) impede the high-temperature application of CaBi₄Ti₄O₁₅ (CBT). In this work, Na⁺/Nd³⁺ co-doped Ca_1−x(Na_1/2Nd_1/2)_xBi₄Ti₄O₁₅ (x = 0-0.12) ceramics were prepared using traditional solid-phase reaction method, and their microstructure and electrical properties were systematically investigated. The results show that with increasing Na⁺/Nd³⁺ co-doping content, the grain size first increases and then slightly decreases. The piezoelectric properties and DC electrical resistivity (ρ_dc) of the ceramic samples first increase and then slightly decrease. At x = 0.09, Ca_0.91(Na_1/2Nd_1/2)_0.09Bi₄Ti₄O₁₅ exhibits a high piezoelectric coefficient (d₃₃ = 24 pC N⁻¹) and high temperature DC electrical resistivity (ρ_dc = 5.6 × 10⁶ Ω cm at 600 °C), as well as a high Curie temperature of 761 °C. The enhancement in overall performance suggests that Na⁺/Nd³⁺ co-doped CBT ceramics are promising candidate materials for high-temperature piezoelectric applications.