Thin-film stabilization of LiNbO3-type ZnSnO3 and MgSnO3 by molecular-beam epitaxy

In polar crystals, cooperative ionic displacement produces a macroscopic spontaneous polarization. Among such polar materials, LiNbO3-type wide bandgap oxides are particularly appealing because they offer useful ferroelectric properties and also potentially lead to multiferroic materials. Using molecular-beam epitaxy, we investigated the thin-film growth of high-pressure phase LiNbO3-type ZnSnO3 and discovered a polar oxide candidate, MgSnO3. We found that LiNbO3-type substrates play an essential role in the crystallization of these compounds, though corundum-type Al2O3 substrates also have the identical crystallographic arrangement of oxygen sublattice. Optical transmittance and electrical transport measurements revealed their potential as a transparent conducting oxide. Establishment of a thin-film synthetic route would be the basis for exploration of functional polar oxides and research on conduction at ferroelectric interfaces and domain walls.