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We have investigated the dislocation of GaN films grown by hydride vapor phase epitaxy (HVPE) on c-plane sapphire substrates using transmission electron microscopy (TEM), etch pit density (EPD) characteristics, and micro photoluminescence (PL). Micro PL mapping is a nondestructive method for observing defect sites as dark spots which reveal the dislocations causing non-radiative recombination centers in the GaN film surface. The dark spots reveal a decrease in threading dislocation sites with increasing the thickness of GaN films. In order to illustrate the correlation between the thickness and the dislocation density of GaN, the micro PL analysis method was used to observe the dislocation densities of a GaN film with a low dislocation density.

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Dielectric properties of polycrystalline BaTiO3 ceramics having grain sizes of 1 to 40 μm have been studied. Fine-grained ceramic BaTiO3 of 1 μm average grain size has 90°domains and has shown higher dielectric constant, lower ferroelectric transition temperature (Tc), and lower transition energy than coarser-grained material. 90°domain switching was preferentially produced in the fine-grained BaTiO3 as a result of abrasion. For the fine-grained BaTiO3, the dielectric constant decreased with one-dimensional pressure, whereas, for the coarse-grained material, the dielectric constant increased before decreasing with the pressure. The one-dimensional pressure resulted in increased Tc of both the fine- and coarse-grained BaTiO3, with the effect being the greatest for the coarse-grained material. The relationship between these results and internal stress, and the effect of external pressure imposed on internally stressed lattice, were discussed.