Combinatorial substrate epitaxy: A high-throughput method for determining phase and orientation relationships and its application to BiFeO3/TiO2 heterostructures

A new technique, combinatorial substrate epitaxy, has been used to study the polymorphic stability and orientation relationships (ORs) for TiO2 thin films grown by pulsed laser deposition on polycrystalline BiFeO3 at 600 °C. Electron backscatter diffraction data from 150 substrate/film pairs were analyzed to determine that anatase (A) grew with the OR (1 1 2)A || (1 1 1)BFO and [11¯0]A||[11¯0]BFO on BiFeO3 (BFO) substrates oriented within 35° of [1 0 0]. Rutile (R) was found on all other substrate orientations with (1 0 0)R || (1 1 1)BFO. The in-plane orientation was primarily [0 0 1]R || [11¯0]BFO, but some films near the anatase/rutile phase boundary were rotated by 30° so that [0 0 1]R || [1¯21¯]BFO. Because these substrate film pairs have high-index interface planes, conventional epitaxy arguments based on two-dimensional lattice mismatch in low-index planes are considered to be limiting cases of a more general model involving the three-dimensional alignment of closest packed planes and directions, regardless of the interface plane.