Room-temperature ferroelectricity in A-site ordered Ruddlesden-Popper Li2CaTa2O7 ceramics

In the present work, the crystal structure, ferroelectric and dielectric properties of the dense single-phase Li2CaTa2O7 ceramics with A-site ordered double-layer Ruddlesden-Popper structures have been investigated by the experiments and first-principles calculations. A polar Pna21 phase was determined by the Rietveld refinement against the X-ray diffraction pattern at room temperature, and it was confirmed by its lowest calculated energy and rigid phonon modes. The ferroelectricity was found by observing the ferroelectric hysteresis loop at room temperature, and its remanent polarization was similar to the value calculated from the Berry phase and Born effective charge approaches. The ferroelectricity is a non-conventional proper one since its polarization is induced from the displacement of oxygen anions instead of tantalum cations based on the individual atomic polarization. A first-order transition from an antiferroelectric to paraelectric phase around 900 K was found by the DSC and variable-temperature dielectric measurements. From the present work, the room-temperature ferroelectricity is experimental confirmed in the present ceramics, inspiring the search for new ferroelectricity in the ceramics with A-site ordered Ruddlesden-Popper structures.