Oxygen on COnductivities of Rhombohedral Phases in The Ba-Sr-Bi OXide System

摘要

The rhombohedral phase of the Ba-Bi-O system is known to be a good oxygen ion conductor. Previous stuides on conductivity of that system have shown that there is succen increase in conductivity at the #beta#_2-#beta#_1 polymorphic transition. Therefore, the high temperature #beta#_2 phase is a very good anionic conductor iwht values up to 10~(-1)-10~0 S/cm. In the Ba-Sr-Bi-O system, the rhombohedral phase that contains Ba and Sr ocexists with BaBIO_3. Several specimens ofthe rhombohedral phase with different [Ba]-[Sr] ratios were synthesized. Electron microprobe analysis was used ot determine the chemical composition of each specimen and to ensure that it ocnsisted of a monophasic assemblage. Results of X-ray powder diffraction experiments confirmed that each sample ahs a rhombohedral unti cell. Oxygen ion conductivities of these materials were measured using th 2-probe AC Impedance technique over the 320-730 deg C temperature range. In each case, a sudden increase in conductivity indicates temperature range of the polymorphic transition. Exchange of the smaller cation Sr for Ba makes the transtion temperature increase almost in a linear manner. Conductivities of all #beta#_2 polymorphs at a given temperature are very similar to conductivigties of Ba-Bi-O and Sr-Bi-O #beta#_2 polymorphs. COnductivities of all #beta#_1 polymorphs are also similar. Apparently, the nature of the alkaline earth present has only slight influnece on conductivities of these phases.