Growth of the 2223 phase has been studied in the leaded Bi-Sr-Ca-Cu-O system. Differential thermal analysis showed that the enhanced formation of the 2223 phase occurs in the temperature range between 835°C and 869°C where partial melting occurs. The density of the pellet was found to increase by 30% at one hour and then to decrease by 40% from the highest density attained. The former is attributed to the growth of the 2223 phase with the aid of the partially melted liquid phase and the latter to the flaky shape of the resultant 2223 crystals. The effect of Pb addition for enhanced 2223 phase formation will be discussed.
The growth process of 2223 phase in a leaded Bi-Sr-Ca-Cu oxide system has been investigated under various oxygen partial pressures using differential thermal analysis, combined with XRD of the quenched specimen. It is shown that under a slow heating rate, the DTA curves exhibit two or three endothermic peaks between 820 to 900°C, and the peak positions are lowered with reduction in the O2 partial pressure. The 2223 phase is found to grow most efficiently in the partial melting state sandwiched between the two endothermic peaks, and the temperature range between the two peaks becomes maximum around 0.1-atm O2 partial pressure.
The electrical conduction mechanism in La3Ta0.5Ga5.5O14 (LTG) was studied from the standpoint of defect formation during growth caused by the nonstoichiometry of the crystal. Since the stoichiometric composition of LTG does not coincide with the congruent composition, single crystals grown from the stoichiometric melt under an atmosphere of O2/Ar in the oxygen partial pressure range from 0.005 to 1 atm was Ta-poor. Ta vacancies were formed during the growth, and their population was predominated by the growth-pO2. With increasing temperature up to 600 °C, the Ta vacancies were ionized to yield holes, and thus the electrical conductivity of the LTG crystal varied with temperature and growth-pO2. In contrast, Ga vacancies as a carrier source would form by Ga evaporation during growth under pO2 below 0.005 atm. The growth-pO2 dependence of the electrical conductivity was opposite to the case for Ta vacancies. For the case of sintered LTG with the exact stoichiometric composition, impurity defects dominated electrical conduction below 600 °C, where the impurity concentration was higher than the cation vacancies arising from the nonstoichiometry of the sintered LTG. Thus, electrical conductivity was almost independent of the sintering atmosphere of pO2. Above 700 °C, the dominant carrier in both single crystal and sintered LTG was ions related to oxygen defects formed by the anion Frenkel reaction.
Silicon dioxide films have been prepared from monosilane and oxygen gases using a low-pressure mercury lamp. The deposition rate is increased with UV irradiation and the activation energy is reduced to as low as 0.22 eV. The contribution of the 254 nm light to the deposition is concluded to be very small. The refractive index of the deposited film is 1.44∼1.46. The infrared absorption peaks related with Si–H bonding do not appear in the photo-CVD film.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.