New class of planar ferroelectric Mott insulators via first-principles design.

The bulk photovoltaic effect requires a low electronic band gap (i.e., ≈1–2 eV) and large electronic polarization, which is not common in known materials. Here we use first-principles calculations to design layered double perovskite oxides AA′BB′O6 which achieve the aforementioned properties in the context of Mott insulators. In our design rules, the gap is dictated by B/B′ electronegativity difference in a Mott state, while the polarization is obtained via nominal d0 filling on the B-site, A-type cations bearing lone-pair electrons, and A≠A′ size mismatch. Successful execution is demonstrated in BaBiCuVO6, BaBiNiVO6, BaLaCuVO6, and PbLaCuVO6.