We optimize the preparation of BZY20 and BCY10 by a wet chemistry route (the polyacrylamide gel process) and mixed oxide route, respectively. For both materials, the purity of powders drastically depends on the annealing conditions of the raw materials. Pure BZY20 powder can be prepared at 1250 degrees C while, for pure BCY10, completion of the reaction is achieved if the raw powder is pressed. After polishing the surface and crushing the bulk of the pellet annealed at 1425 degrees C, pure powder of BCY10 is obtained. Water uptake measurement is leading to values corresponding to an almost complete filling of the oxygen vacancies. Furthermore, we check the sample degradation during sintering of pellets from pure BCY10 and BZY20 powder. Dense ceramic of pure material can be prepared after sintering at 1500 degrees C for 10 h. Above this temperature, a degradation of the pellets both in the surface and the bulk occurs. This paper points out the difficulties in preparing pure BayM1-xYxO3-delta (M= Zr, Cc) for use in electrical characterization or functional for fuel cell technology studies.