Preparation of La0.5Sr0.5CoO3 powders and thin film from a new aqueous solution-gel precursor

This paper reports on the spin deposition of LSCO thin films on a SiO2/Si substrate by a new aqueous solution-gel route. Stable and monometallic precursor solutions are prepared from common and inexpensive oxides or hydroxides. The aqueous La3+ precursor is synthesized by reaction of La2O3 with citric acid. In order to prepare an aqueous Sr2+ precursor Sr(OH)2 is complexed by EDTA. The new peroxo citrato Co2+ precursor is synthesized by reaction of Co(OH)2 with hydrogen peroxide in an aqueous solution of citric acid. Mixing the individual precursors in stoichiometric quantities results in a clear and stable aqueous LSCO precursor solution. Evaporation of water transforms this solution in an amorphous gel that is homogeneous down to nanometer scale. In situ high temperature X-ray diffraction analysis of the gel reveals that phase pure LSCO powder is formed at 550 °C without detection of any intermediate crystalline phase. Spin deposition and crystallization at 625 °C in pure O2 of this aqueous precursor solution resulted in a phase pure conductive LSCO thin film. The sheet resistance of this thin film amounted to 235 Ω/sq. Since the thickness of the film is 120 nm, the specific resistivity was calculated to be 2.8 mΩ cm at room temperature.