Antiferroelectric Phase Transition in Titanite-Type Solid Solutions Na(Nb,Ta)GeO5.

Titanite-type oxides ABMO5 are emerging antiferroelectrics owing to their unique one-dimensional structure. In this study, the predominant role of the B-site off-center displacement on the antiferroelectricity of titanite-type solid solutions Na(Nb,Ta)GeO5 is revealed via dielectric measurements and synchrotron X-ray diffraction experiments. Increasing the Nb concentration led to stronger second-order Jahn-Teller effects and a larger B-site off-center displacement along BO6 chains, resulting in a more stable antiferroelectric state and a higher phase transition temperature. The anisotropy of the titanite-type structure results in a trade-off relationship between stabilizing the antiferroelectric state and observing clear antiferroelectric double-hysteresis loops in polarization-electric field curves. These findings suggest future directions for controlling the titanite-type antiferroelectricity beyond the current B-site substitution strategy.