Thermochemical stability and nonstoichiometry of erbia-stabilized bismuth oxide

A phase study has been performed of high oxygen ion conducting erbia-stabilized bismuth oxide ( 1 -x)Bi203.xEr203 (BElOOx ) using thermal analysis and X-ray powder diffraction. Investigation of the effect of a long-time (500 h) anneal of samples at 650°C in air revealed that the minimum amount of erbia needed to stabilize the high-temperature cubic 8-Biros phase is 27.5 at%. This boundary value is much larger than the one usually reported in literature where the sluggishenss of the transformation from cubic to hexagonal at high Bi contents is not taken into account. Changes in nonstoichiometry of solid solutions Bi,_,Erti03+dbetween 550°C and 850°C upon varying the ambient oxygen partial pressure are minimal for samples with 27.5 at% erbia, increasing with increasing erbia content. The parameter 6 in pure oxygen increases from 0.0044 for BE27.5 to 0.022 for BE50 taking the compo. sition m mtrogen (P,, z lo-’ atm) as stoichiometric reference (850).