(Pb, La) (Zr, Ti) O
3 is a highly transparent ferroelectric ceramic fabricated by doping La into PZT. However, the mechanism to achieve its high transparency has not been adequately clarified yet. In order to substantiate the concept in the preceding study concerning the optical transparency of ferroelectric ceramics PLZT, the optical transparency and the crystal-lattice anisotropy of the hot-pressed Sm-, Sr- and Ba-doped PZT were investigated.
As in the case of PLZT, the optical transmittance of the above ferroelectric ceramics and the anisotropy of individual grains are closely related. That is, the optical transmittance of solid solution system (PbZrO
3-BaZrO
3) increases with the decrease in the lattice anisotropy of grains within the range of ferroelectric phase (BaZrO
3 concentrations: 15-35mol%) in the phase diagram. On the other hand, in the case of the Sm-doped PZT, this tendency was observed only with respect to less concentration than the solubility limit (4 at %) of Sm in PZT. From these results, it was thought that crystal-lattice anisotropy apparently has a great effect on optical transmittance in ferroelectric ceramics, although optical anisotropy directly controls the optical transmittance of polycrystalline solids.
In general, the light scattering in anisotropic ceramics is affected by grain size, optical anisotropy and crystal imperfections such as pores and precipitates. In the PbZrO
3-BaZrO
3 solid soution, the grain sizes were nearly equal, and photomicrographs showed that porosity was negligible. No precipitated second phase was detected by electron microscopy. Therefore, it was suggested that light scattering in the present ferroelectric ceramics is also caused mainly due to the variation in refractive index at domain and grain boundaries as in the case of the PLZT system. In line with the above consideration, the Sr- and Ba-doped PZT were fabricated to highly transparent bodies (transmittance 70%, thickness 0.25mm, wavelength 0.7μm) by the hot-pressing technique (condition: 1400°C, 5h, 150kg/cm
2). This means that the anisotropy of these materials can be decreased by doping Sr or Ba in PZT and consequently the light scattering at domain boundaries is decreased.
The present work suggests that ferroelectric ceramics other than PLZT and modified PLZT can be fabricated to highly transparent substances by decreasing their optical anisotropy and by selecting a sintering process which eliminate pores, to a considerable extent.
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