Greatly improved piezoelectricity and thermal stability of (Na, Sm) Co-doped CaBi2Nb2O9 ceramics

Calcium bismuth niobate (CaBi₂Nb₂O₉) is regarded as one of the most potential high-temperature piezoelectric materials owing to its highest Curie point in bismuth layer-structured ferroelectrics. Nevertheless, low piezoelectric coefficient and low resistivity at high temperature considerably restrict its development as key electronic components. Herein, markedly improved piezoelectric properties and DC resistivity of CaBi₂Nb₂O₉ ceramics through Na⁺ and Sm³⁺ co-doping are reported. The nominal compositions Ca_1-2x(Na, Sm)_xBi₂Nb₂O₉ (x ​= ​0, 0.01, 0.025, and 0.05) ceramics have been prepared via the conventional solid state method. An optimum composition of Ca_0.95(Na, Sm)_0.025Bi₂Nb₂O₉ is obtained, which possesses a high Curie point of ∼949 ​°C, a piezoelectric coefficient of ∼12.8 ​pC/N, and a DC electrical resistivity at 500 ​°C of ∼4 ​× ​10⁷ ​Ω ​·cm. The improved d₃₃ is probably ascribed to the reduction in domain size and the increase in domain wall density caused by the reduced grain size. More importantly, after annealing at 900 ​°C for 2 ​h, the piezoelectric coefficient still maintains about 90% of the initial d₃₃ value, which displays a significant improvement compared to pure CaBi₂Nb₂O₉ ceramic with only 44% of the initial d₃₃ value. This work exhibits a feasible approach to simultaneously obtain high piezoelectric property and thermal stability in CaBi₂Nb₂O₉ ceramics by Na⁺/Sm³⁺ co-doping.