Structural and magnetic inhomogeneity and the NMR of Mn55 and La139 in the magnetoresistive ceramics La0.7Ba0.3−xSnxMnO3→La0.7−xBa0.3−xMnO3+0.5xLa2Sn2O7

• Published in: Low temperature physics (Woodbury, N.Y.) N.Y.), 2003-11, Vol.29 (11), p.910-916
• Main Authors: Pashchenko, V. P., Shemyakov, A. A., Savosta, M. M., Khartsev, S. I., Derkachenko, V. N., Prokopenko, V. K., Turchenko, V. A., Pashchenko, A. V., Dyakonov, V. P., Buhanzev, Yu, Szymczak, H.
• Format: Article
• Language: English
• ISSN: 1063-777X; 1090-6517
• DOI: 10.1063/1.1614235

The effects of substitution of barium by tin on the phase composition, structural imperfection, and properties of lanthanum manganite perovskites La0.7Ba0.3−xSnxMnO3 (x=0, 0.1, 0.15, 0.2, 0.3) are established by comprehensive studies done by x-ray diffraction, resistive, and magnetic (including NMR on Mn55 and La139) methods. It is shown that the introduction of Sn leads to the formation of a pyrochloric phase La2Sn2O7, to an increase in the density of lattice defects of the manganese-enriched main lanthanum manganite phase, and to a substantial decrease of the magnetoresistive effect. The smearing of the metal–semiconductor phase transition temperature is explained by an increase in the inhomogeneity and imperfection of the perovskite structure. The low activation energy is confirmed by a high degree of inhomogeneity and imperfection of the crystal lattice of the samples studied. The broad, asymmetric NMR spectra of Mn55 and La139 attest to high-frequency electron exchange between Mn3+ and Mn4+ and nonequivalence of the environment of those ions and La3+ due both to heterovalent ions and to vacancies and clusters.