Microstructure and properties of sol-gel derived (La,Sr)CoO3 thin film with compositional fluctuation La/Sr ratio

Thin films of Lanthanum strontium cobalite [(La1-xSrx)CoO3, LSCO] were directly spin-coated onto SiO2/Si (100) substrates with compositional fluctuation La/Sr ratio, followed by rapid thermal annealing (RTA). The effects of different La/Sr ratios on the microstructure, surface morphology and electrical properties of the films were examined by X-ray diffraction (XRD), scanning electrical microscopy (SEM) and four probe measurements, respectively. The results indicate that the thin film displays a structure transform from rhombohedral phase to cubic phase around x=0.5, and that the resistivity of the thin film decreases with the increase of La/Sr ratio at the first, then increase slightly. A minimum value of resistivity of LSCO appears at x=0.5. In addition, the effect of the annealing temperature on the electrical properties of La0.5Sr0.5CoO3 films is discussed.