Heteroepitaxial Growth of T-Nb(2)O(5) on SrTiO(3)

There is a growing interest in exploiting the functional properties of niobium oxides in general and of the T-Nb(2)O(5) polymorph in particular. Fundamental investigations of the properties of niobium oxides are, however, hindered by the availability of materials with sufficient structural perfection. It is expected that high-quality T-Nb(2)O(5) can be made using heteroepitaxial growth. Here, we investigated the epitaxial growth of T-Nb(2)O(5) on a prototype perovskite oxide, SrTiO(3). Even though there exists a reasonable lattice mismatch in one crystallographic direction, these materials have a significant difference in crystal structure: SrTiO(3) is cubic, whereas T-Nb(2)O(5) is orthorhombic. It is found that this difference in symmetry results in the formation of domains that have the T-Nb(2)O(5) c-axis aligned with the SrTiO(3) <001>(s) in-plane directions. Hence, the number of domain orientations is four and two for the growth on (100)(s)- and (110)(s)-oriented substrates, respectively. Interestingly, the out-of-plane growth direction remains the same for both substrate orientations, suggesting a weak interfacial coupling between the two materials. Despite challenges associated with the heteroepitaxial growth of T-Nb(2)O(5), the T-Nb(2)O(5) films presented in this paper are a significant improvement in terms of structural quality compared to their polycrystalline counterparts.