Electrical conductivity, oxygen ion transference numbers and thermal expansion of solid solutions Bi(Zr,Y)O-1.5 and Bi(Y,Pr)O-1.5 have been investigated from the standpoint of their use for high temperature oxygen pumps. It has been found that use of solid electrolytes of ternary system Bi2O3-ZrO2-Y2O3, having high ionic conductivity, offers reduction in the polarization resistance of electrochemical cells with silver electrodes, as compared with electrolytes Bi(Y)O-1.5. Formation of continuous series of solid solutions with mixed ionic and electronic conductivity has been ascertained for the system (Bi(1-x)YxO(1.5))(1-y)(PrO1.833)(y) at x=0.25-0.50 and y=0-0.15. Oxygen ion transference numbers for the ceramics containing praseodimia are 0.85+/-0.10. Cermet electrodes containing silver and cobaltites Ln(Sr)CoO3-delta (Ln is a rare earth element) possess much higher electrochemical activity than electrodes containing cobaltite only, and show better mechanical strength in comparison with silver electrodes.