A route to high polarization multiferroics

Large ferroelectric polarizations are usually seen in $d^0$ ferroelectrics, while those with a finite d-electron count usually have a polarization which is two orders of magnitude smaller. The route then to high polarization multiferroics, seems quite obvious - examine if we can stabilize the $d^0$ type distortions in finite d-electron systems. The way we went about this was to dope carriers into BaTiO$_3$ and examine if ferroelectricity survived. Considering the example of V doping in BaTiO$_3$, we found that ferroelectricity was strongly stabilized, much stronger that in the undoped limit. Microscopic modeling coupled with ab-initio calculations revealed that part of the stability of the ferroelectric distortions about the V site emerged from first-order Jahn-Teller effects. The dilute doping limit was used to identify some design principles and helped us to design new multiferroics.