Stabilization of the perovskite phase in the Y-Bi-O system by using a BaBiO${}_3$ buffer layer

A topological insulating phase has theoretically been predicted for the thermodynamically unstable perovskite phase of YBiO${}_3$. Here, it is shown that the crystal structure of the Y-Bi-O system can be controlled by using a BaBiO${}_3$ buffer layer. The BaBiO${}_3$ film overcomes the large lattice mismatch of 12% with the SrTiO${}_3$ substrate by forming a rocksalt structure in between the two perovskite structures. Depositing an YBiO${}_3$ film directly on a SrTiO${}_3$ substrate gives a fluorite structure. However, when the Y-Bi-O system is deposited on top of the buffer layer with the correct crystal phase and comparable lattice constant, a single oriented perovskite structure with the expected lattice constants is observed.