Mechanism of ferroelectric instabilities in non-d0 perovskites: LaCrO3 versus CaMnO3

The incompatibility of partial d occupation on the perovskite B-site with the standard charge transfer mechanism for ferroelectricity has been a central paradigm in multiferroics research. Nevertheless, it was recently shown by density functional theory calculations that CaMnO3 exhibits a polar instability that even dominates over the octahedral tilting for slightly enlarged unit cell volume. Here, we present similar calculations for LaCrO3, which has the same d3 B-site electron configuration as CaMnO3. We show that LaCrO3 exhibits a similar, albeit somewhat weaker, volume-dependent polar instability as CaMnO3, but while the Born effective charge (BEC) for the Mn4+ cation in CaMnO3 is highly anomalous, the BEC for Cr3+ in LaCrO3 is only slightly enhanced. We decompose the BECs for both systems in contributions of individual Wannier functions to elucidate the different driving force behind the polar instability in these systems.