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

Abstract

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 Tf decreased. The shift of the M1–M2 phase transition temperature and Tf 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 EF. 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 EB 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.