Phase Stability of Ln2BaCuO5 (Ln = Dy, Er, Eu, Gd, Ho, Sm, Yb)

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Abstract
Phase stability of a series of Ln2BaCuO5 (Ln=Dy, Er, Eu, Gd, Ho, Sm, Yb) has been studied as a function of oxygen partial pressure and temperature by X‐ray diffraction, thermal gravimetric, and differential thermal analyses. Above the critical temperature Td, phase decomposition with a decrease in sample weight took place. In the case of Ln=Dy, Er, Ho, and Yb, the Ln2BaCuO5 was decomposed into Ln2O3BaCuO3 and BaCuO2. The critical temperature Td (K) was changed depending heavily on the oxygen partial pressure P (Pa) and the effective ionic radius R (0.1‐nm unit) of the Ln atom which was sevenfold coordinated by oxygen atoms. The observed Td values for all of the systems, together with those of Y2BaCuO5 reported previously, closely followed the relation Td=−17493R2+ 34582R − 15489 + 239.47 In P with a reliability index Rp=0.5%. [Key words: superconductors, barium, phases, X‐ray diffraction, differential thermal analysis.]

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