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 (P_r = 1.34 μC/cm² and E_C = 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. [ABSTRACT FROM AUTHOR]