We report on phase studies in the pseudobinary YBa2Cu3O7−δ-BaCuO2 subsystem under oxygen atmosphere with special attention to the influence of the crucible material. We show that different crucibles made from Al2O3 and Y2O3-stabilized ZrO2 respectively lead to different results in the DSC experiments. Our phase diagram data are compared with literature data. With the experience obtained during these investigations, we performed crystal growth experiments in Al2O3 and in Y2O3-stabilized ZrO2 crucibles. The differences of the results are discussed.