Enhancement in hybrid improper ferroelectricity of Ca3Ti2O7 ceramics by a two-stage sintering

Abstract

Ca3Ti2O7 ceramics were prepared by a solid-state reaction process, and the influences of the sintering process on its microstructure and electric properties have been systematically studied. All the ceramic samples fabricated by different sintering processes are single polar A21am phase at room temperature, and the results indicate that the extra calcining or sintering at 1400 °C is beneficial to get the higher lattice constants. Especially the Ca3Ti2O7 ceramics fabricated by the two-stage sintering exhibit the largest rotation angle and tilt angle of the oxygen octahedron, the densest microstructure, and the largest grain size among all the samples. The correlation of crystal structure and hybrid improper ferroelectricity confirms that the amplitude of tilt and rotation of oxygen octahedron is crucial to regulate the remnant polarization of Ca3Ti2O7 ceramics. The leakage behaviors, dielectric and ferroelectric properties of Ca3Ti2O7 ceramics are dependent on the microstructure, oxygen vacancy, and grain size caused by different sintering processes, and the related mechanisms have been illuminated. The highest remnant polarization (1.319 μC/cm2) to our knowledge and the lower coercive field (78.17 kV/cm) was achieved in the ceramic sample fabricated by the two-stage sintering, and these findings have an important significance in developing excellent hybrid improper ferroelectric materials.