Tuning the Strain in LaCoO3 Thin Films by the Heteroepitaxial Growth on Single Crystal Substrates

Abstract

Epitaxial strain in LaCoO3 thin films has been changed by the growth of thin films on different substrate materials, i.e., (001) oriented SrLaAlO4, LaAlO3, SrLaGaO4, (LaAlO3)0.3(Sr2AlTaO6)0.7, and SrTiO3. The films were deposited by pulsed laser deposition. The lattice mismatch of the in-plane lattice parameters between the substrate, a s, and LaCoO3, a b, ∈ = (a s−a b)/a b, ranges from ∈ = −1.32% for the growth on SrLaAlO4 to ∈ = +2.76% for films on SrTiO3. The characterization of the structural properties such as film lattice parameters, unit cell volume and epitaxial strain was carried out by θ/2θ scans and reciprocal space mapping on a two-circle and four-circle x-ray diffractometer, respectively. We succeeded in the growth of single phased (001) oriented LCO films on all the substrate materials. For the lattice parameters of the LaCoO3 films we observed a quasi-elastic behaviour in the range of −1% < ∈ < +2 %. The out of plane lattice parameter c increases and the in-plane lattice parameters a and b decrease nearly linearly with decreasing in-plane lattice parameter a s of the substrate material. This indicates an elastic coupling of the film to the substrate and therefore the possibility to tune the Co-O bond-length and thus the crystal field splitting, Δ CF, by epitaxial strain.