Abstract
Influence of sintering temperature and soaking time on densification of Bi2O3 samples doped with 25%mol Y2O3 was investigated by shrinkage and relative density measurements. Samples were sintered in air at different temperatures in the range of 800 to 1000?C for 24 hr. The results showed that samples sintered at 950?C have the maximum relative density. Several samples were sintered at 950?C for duration of 0 to 36 hr in order to evaluate the effect of soaking time on densification of samples. It was found that the samples were sintered at 950?C for 36hr had higher relative density than others did for smaller time duration X-ray diffraction (XRD) analyses detected ? -Bi2O3 as the sole stable phase in all samples. Scanning Electron Microscopy (SEM) investigation of fractured surface of the samples showed that porosities decrease by increasing of sintering temperature and grow by further increasing of temperature.
Highlights
Bismuth Oxide (Bi2O3) is known to exhibit 4 crystallographic polymorphs
It is known that addition of alio or iso valent ions such as Y2O3, several rare earth oxides or alkaline earth oxides can stabilize the cubic phase at lower temperature [1,2,3,4,5,78]
X-ray diffraction (XRD) analysis of samples that are sintered at temperatures of 600 and 950 oC (Fig. 2), confirms the phase transformation of monoclinic phase to cubic phase at 730 oC according to Fig. 1
Summary
Bismuth Oxide (Bi2O3) is known to exhibit 4 crystallographic polymorphs. The high temperature cubic phase (δ) stable above 730 ̊C and the low temperature monoclinic polymorph (α) stable below 730 ̊C and two metastable phases tetragonal β- Bi2O3 and body center cubic γ- Bi2O3 have been reported [1,2,3,4,5]. The cubic δ phase has CaF2 structure and exhibits very high oxygen ion conductivity due to the high concentration of oxygen vacancies [1,2,3,4, 6,7,8] This phase transforms to the low temperature monoclinic phase during cool down. Δ-Bi2O3 can be used as an electrolyte in solid oxide fuel cells due to its high ion conductivity. We intended to stabilize δ-Bi2O3 at room temperature by addition of 25 mol-percent Y2O3 and study the effect of sintering temperature and soaking time on the sintering behavior of samples using shrinkage and relative density measurements. Sintering in air at 950 ̊C for 0-36 hr. (zero time means that the sample was removed from furnace when the temperature reached 950 ̊C)
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