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 P21ab 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 200–1080 K. The present work sheds light on designing the hybrid improper ferroelectrics in A-site ordered triple-layer Ruddlesden–Popper compounds.