Lin, C. T. (Chhui-Tsu)
M.S. (Master of Science)
Department of Chemistry
Metal powders||Thin films||Manganese compounds||Perovskite||Magnetoresistance||Crystallization
Manganese-based perovskites (Ln[sub 1-x]A[sub x])(Mn[sub 1-y]Fe[sub y])O[sub 3] (where Ln = La, A = Sr) are being investigated, because they have many potential electronic device applications due to their unusual electrical, optical, magnetic and magnetoresistive properties. Manganese-based perovskites are successfully synthesized using a technique developed in our laboratory, called "Deposition from Aqueous Acetate Solution (DAAS)." This novel technique, which involves the preparation of stoichiometric mixtures of metal-acetate precursor solutions, followed by the subsequent firing of these mixtures at relatively low temperature (600°C) for short periods of time , was found to produce crystalline (Ln[sub 1-x]A[sub x])(Mn[sub 1-y]Fe[sub y])O[sub 3] materials as determined by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and magnetic field dependent resistivity measurements. The DAAS method has been used to prepare both powders and thin films of (Ln[sub 1-x]A[sub x])(Mn[sub 1-y]Fe[sub y])O[sub 3]. Powder samples of La[sub 0.83]Sr[sub 0.17]MnO[sub 3] fired from 600 to 900 to 1200°C (while maintaining a constant firing time of 100 minutes) results in an increase in product crystalline size, a sharpening, and a progressively higher temperature of the metallic transition. Samples fired at 1200 °C for 100 minutes are high purity, single phase, and exhibit excellent electrical and magnetic characteristics. Powder samples of (La[sub 0.?]Sr[sub 0.3])(Mn[sub 0.93]Fe[sub 0.07])O[sub 3] fired at 1300 °C are also found to be crystalline, and exhibit excellent electrical and magnetic properties. Thin films of La[sub 0.7]Sr[sub 0.3]MnO[sub 3] deposited onto strontium titanate, sapphire, silicon, and BeO substrates and annealed at 900 °C were also found to be crystalline. The surface nature of substrate was found to influence the growth of thin film crystal structure. These films exhibited sharp metal-insulator transitions, and in the case of La[sub 0.7]Sr[sub 0.3]MnO[sub 3] films on strontium titanate, magnetoresistance was observed at the unusually high temperature of ~360 K. Lattice parameters, magnetic dependent resistivities, metallic and ferrometallic transition temperatures, and magnetization values were measured and shown to be comparable to those of (Ln[sub 1-x]A[sub x])(Mn[sub 1-y]Fe[sub y])O[sub 3] materials prepared by much harsher, conventional solid-state methods. Future work will focus on the optimization of the material compositions and synthetic parameters. The material properties obtained by the analytical, electrical and magnetic measurements will be used to probe the chemistry and mechanism of colossal magneto-resistance. The possible applications of these novel materials will also be investigated.
Yang, Shu-jung, "Preparation, crystallization behaviors, and properties of magneto-resistive powders and thin films" (1997). Graduate Research Theses & Dissertations. 4489.
x, 115 pages
Northern Illinois University
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