The fluorite-type oxygen-ion conducting solid solutions (Bi1-xZrx)(0.85)Y0.15O1.5+delta (x = 0.05 and 0.07) and (Bi0.95Nb0.05)(0.85)Ho0.15O1.5+delta partially decompose at temperatures below 900 K, forming several phases isostructural to delta- and gamma-Bi2O3. Formation of the bcc gamma-Bi2O3-type phases at 770 K leads to a sharp decrease in conductivity. Interaction of the Bi2O3-based solid electrolytes with silver electrodes was observed at temperatures above 850 K, resulting in increasing resistance of the electrochemical cells. Electrodes of platinum and perovskite-type La0.7Sr0.3CoO3-delta were ascertained to exhibit sufficient stability when in contact with the bismuth oxide-based electrolytes in the temperature range of 870-1000 K.