Kwang-Hoon Choi

Solid solubility limits of Al2O3 and Ga2O3 in Gd2O3-doped CeO2

Rare-earth-doped ceria has higher oxygen ion conductivity than Y2O3-stabilized ZrO2 and is a candidate electrolyte for low-temperature operating solid oxide fuel cells [1]. Ceria-based ceramics, however, are difficult to densify below 1600 ◦C [2]. In order to reduce the sintering temperature, several investigators [3–7] studied the role of sintering additives. For studying the role of a sintering additive, the information about the solid solubility limit of the additive is required because the addition of sintering additive up to the solid solubility limit gives a positive effect on the sintering behavior [8–12]. The objective of the present study is to determine the solid solubility limits of Al2O3 and Ga2O3 in Gd2O3doped CeO2 by X-ray diffractometry and scanning electron microscopic measurements. Powders of 10 mol% Gd2O3-doped CeO2 with different concentrations of Al2O3 and Ga2O3 were prepared by the coprecipitation method. A mixed aqueous solution having a composition corresponding to (Ce0.8Gd0.2O1.9)1−x (Al2O3)x (x = 0–0.05) and (Ce0.8Gd0.2O1.9)1−x (Ga2O3)x (x = 0–0.1) was obtained by mixing different aqueous solutions prepared from Ce(NO3)3·6H2O powder, Gd(NO3)3·6H2O powder, Al(NO3)3·9H2O powder, and Ga(NO3)3·xH2O powder, respectively. The salt containing the cations was then coprecipitated by adding an aqueous solution prepared from (NH4)2C2O4·H2O powder and NH4OH into the mixed aqueous solution. The precipitates were washed with distilled water and ethyl alcohol, and dried at 120 ◦C for 1 h. Dried powders were calcined at 700 ◦C for 1 h and crushed into fine powders by ball-milling in ethanol for 24 h. The powders were dried again. After drying, the powders were screened to −325 mesh. The powders of −325 mesh size fraction were uniaxially dry-pressed at 200 MPa. After compaction, the compacts were sintered at 1400 ◦C for 5 h. X-ray diffraction (XRD) technique was employed to identify the phases and to investigate the variation in lattice constant. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis spectroscopy (EDX) were employed to investigate the existing forms of Al2O3 and Ga2O3. Fig. 1 shows XRD patterns of the sintered specimens with different Al2O3 contents. All patterns show the peaks of cubic fluorite type. A series of peaks related with a new phase, however, appear in the case of the specimen containing 5 mol% Al2O3. These peaks are marked as in Fig. 1. The new phase was identified as AlGdO3 phase. The presence of the precipitates was shown in the SEM micrographs of the polished specimens with different Al2O3 contents. The addition of Al2O3 did not result in the precipitation up to 2 mol% Al2O3. For larger additions above 3 mol% of Al2O3, the precipitates were beginning to appear. The precipitates were identified to be Al2O3 phase by EDX analysis. Fig. 2 shows a SEM micrograph and corresponding EDX spectra for the specimen containing 5 mol% Al2O3. The precipitates were spot-scanned for EDX analysis, and the result showed that the specimen contained high Al concentration. These results indicate that Al2O3 reacts with Gd3O3 to form AlGdO3 phase and excess Al2O3 is precipitated. In the cases of specimens with 0, 1, 2 and 3 mol% of Al2O3 additions, the peaks of cubic fluorite type were shown on XRD patterns as shown in Fig. 1, but the peaks due to other phase were not detected probably because of the presence of a small amount. The XRD peaks of the solid solutions of Gd2O3doped CeO2 were slightly shifted to higher angle with increasing Al2O3 content. This shift was found by the addition of Al2O3 to the solid solutions of Gd2O3doped CeO2 up to 2 mol% of Al2O3, but the peaks were not shifted by the addition above 3 mol% Al2O3. Fig. 3 shows the lattice constant as a function of Al2O3, which is calculated by using high-angle XRD patterns. The lattice constant decreases linearly with increasing Al2O3 content up to 2 mol%. However, when the content of Al2O3 is over 2 mol%, the lattice constant does not decrease further and become constant. The decrease in lattice constant is considered to be due to the substitution of smaller Al3+ ions (0.53 A) [13] for Ce4+ ions (0.97 A) [14] in the CeO2 structure. Thus the solid solubility limit of Al2O3 in Gd2O3-doped CeO2 is estimated to be 2 mol%. In the case of the specimens with the addition of Ga2O3, XRD measurements were carried out on the specimens with different Ga2O3 contents up to

A Study of Long Term Recording Reserved Type Material by Using Glass Micro-structure

Recently, there are a lot of study to alternate polycarbonate which is being used as storage material in CD, DVD. In this study, we alternated polycarbonate with glass. We observed the change of shape in a surface of the glass which was focused by Nd:YAG Laser. The change of shape and property was studied by thermal mechanical analysis (TMA), UV-Vis spectrometer, AFM and SEM. According to Laser power and quantity of additives, the Bump`s size and shape are showed differently. In high energy, the Bump will be transformed into Pit. And also according to CTE, and absorption ratio of glass, difference between Bump and Pit is confirmed. From these investigation, we could control that the minimum size of bump which is more useful shape than pit`s is about 1.3 m, H 70 nm, and it is near same the spot size.