The formation of a rocksalt structure to overcome the large lattice mismatch between BaBiO3 and SrTiO3

Complex oxides form a material class in which a wide range of properties is observed. The large tunability and high level of control during the growth process are important advantages of this material class and make it possible to influence the electronic and magnetic properties. Different material compositions can be stacked as heterostructures of thin films [1]. However, when subsequent layers have a too large lattice mismatch, the growth cannot continue epitaxially and the crystal quality of the film decreases. To overcome large lattice mismatches, buffer layers are widely adapted [2]. In this work stoichiometric, single oriented BaBiO3 thin films are grown on a SrTiO3 substrate without the use of a buffer layer, even though a 12% lattice mismatch is present. With high resolution scanning transmission electron microscopy (HRSTEM) and geometric phase analysis it is visualized that the large lattice mismatch between BaBiO3 and SrTiO3 is accommodated by a rocksalt structure that forms between the two perovskite compounds. The dislocation that appears every ninth unit cell is consistent with the 12% lattice mismatch [3]. Since the lattice constant of BaBiO3 is quite large for a perovskite crystal phase (a = 4.35 Å), this complex oxide itself is also suitable to function as a template for other perovskite structures. In the same article [3], we show that by using BaBiO3 as a buffer layer material, the Y-Bi-O system is stabilized in the perovskite structure while this is not the most energetically favourable crystal phase.

[1] M. O’Sullivan et al., Nat Chem. 8(4), 292-4 (2016)
[2] G.H. Lee et al., APL Materials 4, 126106 (2016)
[3] R.L. Bouwmeester et al., Phys. Status Solidi RRL, 201800679 (2019)