Optimization of sintering process and enhanced hybrid improper ferroelectricity of Ca3Ti2O7 ceramics fabricated by an acetic acid sol–gel method

The Ca3Ti2O7 materials exhibit hybrid improper ferroelectricity due to the rotation and tilt coupling of TiO6 octahedron. However, the lower remnant polarization of Ca3Ti2O7 ceramics obtained by conventional solid-state method limits its practical application. Herein, the single-phase Ca3Ti2O7 ceramics with enhanced ferroelectricity were synthesized using an acetic acid sol–gel method and two-stage sintering. The sintering process does not significantly change the distortion amplitude of TiO6 octahedron in Ca3Ti2O7 ceramics but has a greater impact on the grain size and the concentration of oxygen vacancy. The synergistic effects of grain size and oxygen vacancy have been achieved in the Ca3Ti2O7 ceramics prepared by the optimal sintering process (1400 °C/12 h − 1550 °C/18 h), which leads to its enhanced hybrid ferroelectricity (Pr = 1.34 μC/cm2 and EC = 120 kV/cm). These findings demonstrate that the sol–gel method is an effective approach to obtain the Ca3Ti2O7 materials with enhanced hybrid improper ferroelectricity.