  We report density functional studies of electron rich interfaces between
KTaO3 or KNbO3 and CaSnO3 or ZnSnO3 and in particular the nature of the
interfacial electron gasses that can be formed. We find that depending on the
details these may occur on either the transition metal or stannate sides of the
interface and in the later case can be shifted away from the interface by
ferroelectricity. We also present calculations for bulk KNbO3, KTaO3, CaSnO3,
BaSnO3 and ZnSnO3, showing the different transport and optical properties that
may be expected on the two sides of such interfaces. The results suggest that
these interfaces may display a wide range of behaviors depending on conditions,
and in particular the interplay with ferroelectricity suggests that electrical
control of these properties may be possible.
