Single-crystal rare earths manganites La_(1-x-y)Bi_xA_yMn_O_(3±β) (A = Ba, Pb): Crystal structure, composition, and Mn ions valence state. X-ray diffraction and XPS study

摘要

Single crystals of La_(1-x-y)Bi_xMn_O_(3±β) and La_(1-x-y)Bi_xA_yMn_O_(3±β) (A = Ba, Pb) are grown, their crystal and electron structure is studied. Relative Mn~(3+)/Mn~(4+) abundance in each single crystal is determined via fitting experimental Mn2p-spectra with weighted superposition of theoretical spectra of tri- and quadrivalent Mn, and, for barium-free samples, from energy splitting of the Mn3s-spectra components. Strong heterogeneousness of the crystals both in elemental composition and crystal structure is discovered. It is shown that the heterogeneousness displays itself in various oxygenic environments around Mn atoms which give rise to the appearance of Mn~(4+) ions. A simple model is proposed that allows understanding the nature of the appearance of Mn~(4+) ions in single crystals of lanthanum-bismuth manganites.