Preparation of La 0.5Sr 0.5CoO 3 powders and thin film from a new aqueous solution–gel precursor

Abstract

This paper reports on the spin deposition of LSCO thin films on a SiO 2/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 La 3+ precursor is synthesized by reaction of La 2O 3 with citric acid. In order to prepare an aqueous Sr 2+ precursor Sr(OH) 2 is complexed by EDTA. The new peroxo citrato Co 2+ 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 O 2 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.