Investigation of the Properties of Ferroelectric Thin/thick Films in the Plzt System.
This study is centered around the characterization of La modified lead zirconate-titanate (PLZT) films in terms of their ferroelectric and electrooptic properties. A metal acetate precursor system was used to dip coat transparent substrates at processing temperatures ranging from 500 ^circC to 700^ circC. The resulting microstructure and film strain were correlated with the film properties in an attempt to understand the special problems associated with chemical deposition techniques and thin film geometry. It was found that depending on composition, an additional phase identified as a lead deficient pyrochlore, forms during the crystallization process in amounts proportional with increasing Zr/Ti ratio. In such cases, excess PbO beyond that calculated for stoichiometric formulations was necessary in order to produce single phase perovskite films. PLT films were shown to crystallize in the perovskite phase more readily than compositions with higher Zr content making them useful as prenucleating buffer layers. A variation in film microstructure with film thickness was cited as the most predominant influence of sample geometry on observed properties. A comparison of microstructural morphology between films on sapphire with those on PLZT plates indicate that the influence of the substrate on the growth processes of the film diminish at ~ 1mum. Uniform film strain measured in a direction normal to the film plane was calculated based on the interplanar d-spacings obtained from X-ray diffraction data. The film strain of PLZT 0/65/35, 9/65/35 and PLT 14/0/100 films was determined and compared with electrooptic and ferroelectric properties. The thermal contribution to the birefringence of the films was subtracted from the total measured birefringence to better understand the effects of film strain on the electrically induced birefringence. It was found that greater shifts in birefringence with applied electric field in the plane of the film were produced when the uniform film strain normal to the film plane is in a relative state of compression. An explanation of this behavior is proposed by describing the material as having both ferroelectric and paraelectric phase regions which are subject to preferential domain alignment coincident with a tension axis.
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- Engineering: Electronics and Electrical; Engineering: Materials Science; Physics: Optics