Hybrid improper ferroelectricity in A-site cation ordered Li2La2Ti3O10 ceramic with triple-layer Ruddlesden-Popper structure

Hybrid improper ferroelectricity has been extensively studied in double-layer Ruddlesden-Popper oxides in recent years. Although the hybrid improper ferroelectricity could be created among triple-layer Ruddlesden-Popper oxides with an ordered A-site cation predicted by the first-principles calculations, no experimental result has been reported yet. In the present work, the room-temperature ferroelectricity has been observed in Li2La2Ti3O10 ceramics with an A-site cation ordered triple-layer Ruddlesden-Popper structure. The polar phase P2(1)ab has been determined by combining the first-principles calculation and the powder diffraction analysis at room temperature. The hybrid improper ferroelectricity was induced by the triple-coupled irreps including the A-site cation ordering. The variable temperature differential scanning calorimetry measurements and dielectric responses indicate no evidence of phase transition over the temperature range of 200-1080K. The present work sheds light on designing the hybrid improper ferroelectrics in A-site ordered triple-layer Ruddlesden-Popper compounds.