Alkoxide route to La0.5Sr0.5CoO3 epitaxial thin films on SrTiO3

An all alkoxide based sol-gel route was investigated for preparation of epitaxial La0.5Sr0.5CoO3 (LSCO) films on 100 SrTiO3 (STO) substrates. Films with 20-30 to 80-100 nm thickness were prepared by spin-coating 0.2-0.6 M (metal) solutions on the STO substrates and heat treatment to 800 degrees C at 2 degrees C min(-1), 30 min, in air. The films were epitaxial with a cube-on-cube alignment and the LSCO cell was strained to match the STO substrate of 3.905 angstrom closely; a and b = 3.894 angstrom and 3.897 angstrom for the 20-30 and 80-100 nm films, respectively. The c-axis was compressed to 3.789 angstrom and 3.782 angstrom for the 20-30 and 80-100 nm films, respectively, which resulted in an almost unchanged cell volume as compared to polycrystalline film and nano-phase powders prepared in the same way. The SEM study showed mainly very smooth, featureless surfaces, but also some defects. A film prepared in the same way on an alpha-Al2O3 substrate was dense and polycrystalline with crystallite sizes in the range 10-50 nm and gave cubic cell dimensions of a(c) = 3.825 angstrom. The conductivity of the ca 30-40 nm thick polycrystalline film was 1.7 m Omega cm, while the epitaxial 80-100 nm film had a conductivity of around 1.9 m Omega cm. (C) 2007 Elsevier B.V. All rights reserved.