The effects of postdeposition heat-treatment on the morphology and microstructure of thin-film CdTe grown by electrodeposition on CdS/Sn02/glass substrates have been investigated. Scanning electron microscopy analysis indicates that the grains of as-deposited CdTe thin films have a faceted morphology with an average grain size of -0.4 p.m. After annealing, the facets become less well-defined and the tops of the grains become domed or rounded. Grain growth studies indicate that the grain growth exponent n is smaller than the usual value of 0.5. X-ray diffraction (XRD) measurements confirm that as-grown CdTe thin films have a zinc-blende structure with a strongly preferred orientation such that the cubic <111> directions are perpendicular to the film plane while annealed CdTe thin films show near-random orientations, indicating that recrystallization occurs during the heat-treatment. The dynamics of recrystallization was investigated by using the ratio of integrated intensities of XRD peaks as an indication of the degree of recrystallization. It was observed that the orientation first tends toward randomness upon annealing but for longer time anneals tends to a preferred orientation of the cubic <111> axes again. The recrystallization activation energy was determined to be 2.5 0.3 eV. The presence of CdC12 in the postdeposition annealing process was observed to accelerate the recrystallization. The residual stress in CdTe films as a function of annealing temperature and time was determined and the type of residual stress changed from compressive to tensile during the annealing.
Ba1−xSrxTiO3 (x = 0.9) ferroelectric ceramics were prepared successfully using a new wet technique and their structure and dielectric properties compared with those synthesized by the solid-state reaction method. The voltage dependence of the dielectric constant in the paraelectric phase was examined. It was found that the dielectric constants of these materials, prepared by both methods, exhibit large changes with applied voltage in the paraelectric phase. Tunability (the percentage change of the dielectric constant from its zero-bias value in the presence of a de-biasing electric field) was observed to exceed 30% at only 1.7 kV/cm at 77 K in the samples prepared by the solid-state reaction method. The tunability was found to decrease dramatically as the operating temperatures increased above the Curie point. These observations are interpreted in light of an existing phenomenological theory. The dependence of the dielectric constant in the paraelectric state upon a de-biasing electric field is also demonstrated as a potential method for the characterization of dielectric nonuniformities in ferroelectric ceramics.
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