The syntheses of superconducting YBCO powders, prepared by solid state reaction, vacuum pyrolysis of acetates, spray pyrolysis of acetates and calcinated oxalates were performed. All of the powders in a paste form were deposited on the Al2O3 substrate. After sintering and annealing the obtained superconducting YBCO thick layers were examined in different (CO2 + O-2) atmospheres. The thermogravimetric as well as IR spectroscopy and SEM study confirm that on the grain boundaries the BaCO3 phase is formed. The presence of BaCO3 phase may cause degradation of superconducting materials.