Effects of Fluorination and Oxygen Deficiency on the Properties of CaMnO_3-y and LaCaMnO_3-y

Electrical conductivity is a property which is important for several technological applications of thin films of functional metal oxides materials. Our project aimed to develop methods to engineer the electrical conductivity of two such materials, Calcium Manganese Oxide CaMnO3 (CMO) and Lanthanum-Calcium Manganese Oxide (LCMO) by introducing oxygen vacancies, or in other words, by making the m 'oxygen deficient'. A second related goal was to make the changes in conductivity more stable by introducing fluorine into the material by a process called spin coating fluorination (SCF). Fluorine is expected to occupy the oxygen vacancy sites or replace some of the existing oxygen. Either of these processes is expected to change electrical conductivity. In our experiments, we grew CMO and LCMO thin films of varying thickness on LAO substrates using the technique of Pulsed Laser Deposition (PLD). We varied the experimental conditions during film growth as well as the thickness of the film to examine how these changes affect the properties of the CMO and LCMO thin films. Properties of interest in this project are crystal structure and electrical resistivity (which is the inverse of electrical conductivity). When oxygen content is reduced, or when fluorine occupies oxygen or oxygen vacancy sites, the crystal lattice is expected to expand, resulting in larger spacings between atomic planes which can be measured with x-ray diffraction. Oxygen vacancies are expected to also increase electrical conductivity, i.e., decrease electrical resistivity. By studying both crystal structure and electrical resistivity of the as grown and fluorinated films, we have obtained information needed to optimize film growth conditions and film thickness for introducing oxygen deficiency and to optimize the conditions for the fluorination process.