Homogeneity ranges of rare-earth manganites with hexagonal crystal structure A2–x Mn x O3±δ (A = Sc, Y, Ho, Er, Tm, Yb, Lu) in air

Abstract

Homogeneous solid solutions and heterogeneous compositions of the general formula Ln2–xMnxO3±δ (Ln = Tm, Lu) were prepared by ceramic synthesis from oxides in the temperature interval 900–1400 °C in air. The homogeneity ranges of thulium and lutetium manganites with respect to metals were determined using X-ray phase analysis. The results obtained are presented in the form of portions of the phase diagrams of the Ln—Mn—O (Ln = Tm, Lu) systems. The phase diagrams are compared with each other and with other available phase diagrams of the systems X—Mn—O (X = Sc, Y, Ho, Er, Yb) where rare-earth manganites with hexagonal crystal structure are formed. Possible reasons for the solubility of rare-earth element and manganese cations in these manganites are discussed. The dependences of the solubility of rare-earth element and manganese cations in the manganites AMnO3±δ (A = Sc, Y, Ho, Er, Tm, Yb, Lu) on the effective ionic radii of A3+ cations, on the number of 4f electrons in these cations, and on the atomic number of the rare-earth element in Mendeleev´s periodic table were constructed. None of these factors unambiguously governs the solubilities in question.