Homogeneity regions of yttrium and ytterbium manganites in air

Homogeneous solid solutions and heterogeneous systems of the general formula R 2 − x Mn x O 3 ± δ (0.90 ≤ x ≤] 1.10 for R = Y and 0.88 ≤ x ≤ 1.14 for R = Yb; Δ x = 0.02) were produced by ceramic synthesis from oxides in air within the temperature range 900–1400°C. The solubility boundaries of simple oxides R 2 O 3 (R = Y, Yb), Mn 3 O 4 , and binary oxide RMn 2 O 5 in yttrium and ytterbium manganites RMnO 3 ± 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 Y 2 O 3 and Mn 3 O 4 in YMnO 3 ± δ was found to increase with increasing temperature, and the solubility of Yb 2 O 3 and Mn 3 O 4 in YbMnO 3 ± δ to be insensitive to varying temperature. It was suggested that the solubility of Y 2 O 3 and Mn 3 O 4 in YMnO 3 ± δ and of Yb 2 O 3 and Mn 3 O 4 in YbMnO 3 ± δ is caused by crystal structure defects of yttrium and ytterbium manganites and their related oxygen nonstoichiometry. In dissolving RMn 2 O 5 in RMnO 3 ± δ (R = Y, Yb) in air within a narrow (∼20°C) temperature range adjacent to the RMn 2 O 5 = RMnO 3 + 1/3Mn 3 O 4 + 1/3O 2 equilibrium temperature, the solubility of RMn 2 O 5 in RMnO 3 ± δ ecreases abruptly until almost zero. Conclusion is made that structural studies are necessary necessary to determine the oxygen nonstoichiometry δ of R 2 − x Mn x O 3 ± 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.