Ageing Phenomena in La-Sr Manganites with Divalent Substituents for Manganese

Abstract

Variations of electromagnetic and structural characteristics of La1¡c xSrc¡xMn1¡xMexO3 γ manganites (Me = Zn, Ni) during storage time up to 36000 hours at room temperature and after frequentative thermal cycling in the 300-573 K range were investigated. Changes of magnetization of all samples were within the error of measurement. In most cases Curie point (TC) showed irregular variations within the range of 20%, while zinc-substituted manganites with relatively high values of "c" exhibited some trend of TC rise. The resistance of all samples increased during storage period. The cell volume of single-phase manganites decreased over time, that may indicates an increase in oxygen content. However, the sample with the highest Ni content (x 0.125) at c 0.19 suffered phase transition "rhombohedral-orthorhombic structures", which cannot be explained by the oxygen absorption. Probably, this effect was due to the rearrangement of the ions and vacancies between crystal sublattices of manganite.