text: A number of other unexpected applications have been identified in the last few years, mostly in multiferroic bismuth ferrite, that do not seem to be directly related to the coupled magnetism and ferroelectricity. These include a photovoltaic effect,  photocatalysis, and gas sensing behaviour. It is likely that the combination of ferroelectric polarisation, with the small band gap composed partially of transition-metal d states are responsible for these favourable properties.
  Multiferroic films with appropriate band gap structure into solar cells was developed which results in high energy conversion efficiency due to efficient ferroelectric polarization driven carrier separation and overband spacing generation photo-voltage. Various films have been researched, and there is also a new approach to effectively adjust the band gap of the double perovskite multilayer oxide by engineering the cation order for Bi2FeCrO6.