Antiferroelectricity in new silver niobate lead-free antiferroelectric ceramics (1-x)AgNbO3-xCaZrO3 (x = 0.00–0.01)

The critical need for clean energy has led to the development of lead-free electroceramics. However, lead-free antiferroelectrics seldom have been reported because of the difficulties in materials fabrication and their low electrical performance. In this work, we successfully synthesized lead-free antiferroelectric ceramics (1-x)AgNbO₃-xCaZrO₃ (x = 0.00–0.01) using the solid state reaction method in flowing oxygen (O₂) atmosphere. Calcium zirconate (CaZrO₃) dopant effectively stabilized the antiferroelectricity of silver niobate (AgNbO₃) by dramatically decreasing the tolerance factor t. Additionally, we identified an orthorhombic Pbcm structure similar to that of pure AgNbO₃. With the introduction of CaZrO₃, phase transition temperatures M₁–M₂, M₂–M₃ and the freezing temperature T_f decreased. The shift of the M₁–M₂ phase transition temperature and T_f was the result of the restriction of the M₁ phase due to CaZrO₃ substitution. The compositions of x < 0.001 displayed a double hysteresis loop with a raised critical field E_F. However, when the doping concentration exceeded 0.002, the double hysteresis loop with a higher polarization could not be obtained until the breakdown strength of E_B exceeded 200 kV/cm because of the tremendously enhanced free energy barrier between the virgin antiferroelectric state and the field-induced ferroelectric state. We also evaluated the polarization hysteresis loops are also evaluated at temperatures up to 100 °C for the compositions x = 0.00–0.005. With an elevated temperature, at which the free energy barrier was reduced, the double hysteresis loop was obtained at a lower electric field when compared with that at room temperature for the compositions x = 0.004 and 0.005. These results demonstrated that by adjusting the tolerance factor t and average electronegativity difference X, the antiferroelectricity could be predicted in AgNbO₃-based lead-free solid solution systems, thus providing a new strategy for designing a new class of antiferroelectric materials.