• Applied Microscopy
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• v.32 no.3
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• pp.257-263
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• 2002

Microstructural investigations of $(Li_{1/2}Pr_{1/2})TiO_3$ (LPT) complex perovskite compounds were carried out using X-ray diffractometry and transmission electron microscopy. LPT has not only the ordering of A-site cation deficiencies but also has the antiphase and inphase tilting of oxygen octahedron and the antiparallel shift of cations. Both the antiphase boundaries and the ferroelastic domains are present in the microstructure. Spinodal decomposition is found in the microstructure. The measured dielectric properties were ${\varepsilon}_r=84.6,\;Q\;{\Large f}_o=776\;GHz,\;{\tau}_{f}=-233.66ppm/^{\circ}C$.

• Applied Microscopy
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• v.34 no.2
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• pp.113-120
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• 2004

Microstructural characteristics of the Complex Perovskite (1-x) $(Li_{1/2}Sm_{1/2})TiO_3-x (Na_{1/2}Sm_{1/2})TiO_3$ (LNST) system have been investigated using the transmission electron microscopy (TEM). When $0.0{\leq}x{\leq}0.6$, the vacancy ordering forming the 1/2 (001) superlattice reflections due to the A-site cation deficiencies has apperaed. It could be confirmed by presence of ABPs. But it was difficult to form the vacancy ordering since vacancy concentration gradually lowered as the amount of the substituted Li ions decrease. Antiphase boundaries (APBs) were presented in microstructures of LNST when $0.8{\leq}x{\leq}1.0$. It was considered that these boundaries were caused by the 1:1 chemical ordering of A-site cations, Na and Sm ions. LNST had not only the antiphase tilting of oxygen octahedron but also the inphase tilting of oxygen octahedron and the antiparallel shift of cations all of them. It could be confirmed by presence of ferroelastic domains

• Restorative Dentistry and Endodontics
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• v.26 no.2
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• pp.180-187
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• 2001

The structure of current guides is largely illogical and without any rational use of color ordering. The shade guides are generally made of plastic (rather than the actual composite material) and do not accurately depict the true shade. translucency. or opacity of the composite resin after polymerization. To solve this problem, information based on evaluations of natural teeth and material that use the same method and experimental conditions is necessary. The present investigation measured the color of natural maxillary anterior teeth in vivo and compared the results with those of composite resins. 269 Korean subjects were selected for this study. Intact central incisor. lateral incisor. and canine were selected. The clinical crowns were free of caries or restorations. The middle site of the coronal portion on the labial surface of the tooth was measured by Chroma Meter. The five light activated. resin-based materials (Amelogen, Denfil, Elitefil, Spectrum, Z100) were used in this study. Resin composite was condensed into plastic mold with a diameter of 8mm and a thickness of 4mm. pressed between glass plates to flatten the surfaces. and polymerized using a Visilux II visible light activation unit. The surfaces were polished sequentially on wet sandpaper. Color measurements of each specimen were accomplished by Chroma Meter. A computer program that compares each tooth color with each composite resin color was written and the minimum CIELAB color difference ($\Delta$E$^*$) between tooth and each material was calculated. Under the conditions of this study: 1. Teeth tend to become darker with advancing age. 2. Canines were darker. more yellow. and less green than incisors. 3. The teeth from the women were lighter. more green. and less yellow than the male teeth. 4. In general. composite resins were lighter. more green. and less yellow than teeth. Deficiencies were noted in Hues in YR range. 5. Mean color differences between the five composite resin products and teeth were detectable to the naked eye($\Delta$E$^*$>1.0). 6. In comparing the mean $\Delta$E$^*$ values of materials. Spectrum showed the least followed by Z100, Elitefil, Amelogen, Denfil in increasing order.