Sol Gel and Spray Pyrolysis

Chemical deposition has been widely used to prepare oxide films, such as ferroelectrics and semiconductor films [37], since it is a fast and cost-efficient preparation method. In nebulized spray pyrolysis, a solution containing the organic derivatives of the relevant metals in a suitable solvent is nebulized by making use of a CMR transducer. The nebulized spray is slowly deposited on a solid substrate at a relatively low temperature, with sufficient control of the rate deposition to yield the oxide of the desired stoichiometry [38]. This technique is a simple and effective route to prepare oriented, stoichiometric oxide films. To prepare CMR films by sol-gel, a stock solution is prepared from acetates of La, Ca, and Mn in appropriate molar ratio (La:Ca:Mn = 0.67:0.33:1 to make a film with a composition La0 67Ca033MnO3) which is dissolved into 2-methoxyethanol. With the addition of H2O, the solution is refluxed at low temperature (80 °C) for 24 h and then aged at room temperature for several days. Xerogel is then obtained though further distillation and drying. The thin films are fabricated using a spin coater, from stock solution spun on a substrate. The films are finally pyrolyzed on a hot plate at 400 °C after each coating, which is repeated to achieve appropriate thickness. Annealing is sometimes necessary to obtain the optimum properties. One can obtain homogeneous thin films and the processing temperature is considerably lower than conventional methods. Good quality CMR thin films have been prepared by these two methods: nebulized spray pyrolysis [39] and sol-gel [40].

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