La(1-x)SrxCoO3 for thin film thermocouple applications

In this study, the LSCO (lanthanum strontium cobalt oxide) family has been investigated for thin film thermocouple applications. Thin films of La(1-x) SrxCoO3 (x = 0.3, 0.5, 0.7) were prepared on sapphire substrates by pulsed laser deposition. The films were annealed at different temperatures in air and characterized for phase, composition and microstructure to determine th eir thermal stability. From the phase and composition analyses, it is clear that as the Sr content in LSCO increases, the thermal stability decreases. Among the three compositions studied, x = 0.3 had the best phase and chemi cal stability, and microstructural properties. It was observed that La0.7Sr 0.3CoO3 possesses excellent phase, composition and microstructural stabilit y up to 1273 K. Above 1273 K,however, LSCO decomposes resulting in the loss of cobalt and formation of individual oxide phases. Electrical resistivity and Seebeck coefficients were measured in situ as a function of temperatur e in air up to 1023 K. The electrical and Seebeck coefficient properties we re found to be stable for all the three compositions up to 1023 K and studi es indicated that electrical conduction occurs through a small polaron hopp ing mechanism. In conclusion, LSCO possessed good thermal stability in air up to 1273 K and exhibits excellent potential in thin film thermocouple app lications. (C) 1999 Elsevier Science S.A. All rights reserved.