Homogeneity regions of yttrium and ytterbium manganites in air |
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Authors: | O M Fedorova V F Balakirev Yu V Golikov |
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Institution: | 1.Institute of Metallurgy, Ural Branch,Russian Academy of Sciences,Yekaterinburg,Russia |
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Abstract: | Homogeneous solid solutions and heterogeneous systems of the general formula R2 − x
Mn
x
O3 ± δ (0.90 ≤ x ≤] 1.10 for R = Y and 0.88 ≤ x ≤ 1.14 for R = Yb; Δx = 0.02) were produced by ceramic synthesis from oxides in air within the temperature range 900–1400°C. The solubility boundaries
of simple oxides R2O3 (R = Y, Yb), Mn3O4, and binary oxide RMn2O5 in yttrium and ytterbium manganites RMnO3 ± δ were determined X-ray powder diffraction of these solutions and systems. The results were presented as fragments of phase
diagrams of the systems Y-Mn-O and Yb-Mn-O in air. The solubility of Y2O3 and Mn3O4 in YMnO3 ± δ was found to increase with increasing temperature, and the solubility of Yb2O3 and Mn3O4 in YbMnO3 ± δ to be insensitive to varying temperature. It was suggested that the solubility of Y2O3 and Mn3O4 in YMnO3 ± δ and of Yb2O3 and Mn3O4 in YbMnO3 ± δ is caused by crystal structure defects of yttrium and ytterbium manganites and their related oxygen nonstoichiometry. In
dissolving RMn2O5 in RMnO3 ± δ (R = Y, Yb) in air within a narrow (∼20°C) temperature range adjacent to the RMn2O5 = RMnO3 + 1/3Mn3O4 + 1/3O2 equilibrium temperature, the solubility of RMn2O5 in RMnO3 ± δ ecreases abruptly until almost zero. Conclusion is made that structural studies are necessary necessary to determine the
oxygen nonstoichiometry δ of R2 − x
Mn
x
O3 ± δ solid solutions as a function of x and synthesis temperature; together with the results of this work, these studies will allow one to construct unique crystal-chemical
models of these solid solutions. |
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