YBA2FE3O8 AND THE YCU(O)-BACU(O)-YFE(O)-BAFE(O) PHASE-DIAGRAM

Subsolidus phase relations are given under pseudo-isothermal conditions (910-950°C) for the YCu (O){single bond}BaCu(O){single bond}YFe(O){single bond}BaFe(O) square section of the Y(O){single bond}Ba(O){single bond}Cu(O){single bond}Fe(O) tetrahedral phase diagram. All samples are prepared from liquid-mixed citrate precursors, ensuring a relatively rapid establishment of equilibrium and high compositional resolution. A new phase, tetragonalYBa2Fe3O8+w (w ∼ 0.07 when saturated in 1 atm oxygen), witha = 391.67(3) andc = 1181.78(12)pm, is synthesized and its stability limits toward the alternative formation of a disordered perovskite [a = 399.58(5)pm] are given. A total of 8(1)% of the Fe atoms in YBa2Fe3O8 can be replaced by Cu, which may be comparable to the situation for the YBaCuFeO5 phase [13(5)%]. Up to 17(5)% of the Cu atoms in YBaCuFeO5 can be replaced by Fe, as compared to 22(2)% for YBa2Cu3O7 and some 20% for BaCuO2. The existence of a large homogeneity envelope, originating at a perovskite-type BaFe1-zYzOw phase with az variable around 0.10 andw ∼ 2.6, is found from mole-balance calculations of phase content. The homogeneity envelope comprises up to 20(5)% Cu for Fe substitution or up to 10(5)% Y for Ba substitution depending on the simultaneous presence of Y at the Fe site. © 1992 Academic Press, Inc. All rights reserved.