Topological ferroelectricity in layered perovskite LaTaO4: A first principles study

The ferroelectricity in layered perovskite LaTaO4 is investigated by first-principles calculations. The rather large polarization (about 36 μC/cm2) along -c direction is obtained by the Berry phase approach. Ferroelectric phase can be induced by freezing a soft B1u mode from the prototype phase, and this mode involves the rotations of oxygen octahedron and the displacement of La3+ cations. The topological ferroelectricity is adopted based on the previous work to distinguish from the typical proper ferroelectrics, such as BaTiO3. The 0 K stable monoclinic phase can be regarded as an antiferroelectric phase since the polarization of the neighboring layer will be canceled each other. However, the ferroelectric phase is metastable because of the unexpected small barrier between paraelectric and monoclinic phase and narrow energy gap between ferroelectric and monoclinic phase, and this result can explain the previous experimental results. From the present work, the topological ferroelectricity in layered perovskite LaTaO4 is confirmed, and the rather high polarization makes the present compound as a promising candidate for the lead-free ferroelectric application.