Phase transitions in manganites with substitution of divalent ions for manganese

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

“…Of great interest is the phenomenon of phase conversion from rhombohedral to orthorhombic structure in Nicontained compositions with x 0.125 after long-term storage. Such conversion may not be directly related to the oxygen absorption, because excess of oxygen content promotes the existence of rhombohedral phase [10]. Actually, after annealing under conditions resulting in stoichiometric oxygen content [8,10,11], this manganite became orthorhombic with v 59.29 Å 3 .…”

“…Such conversion may not be directly related to the oxygen absorption, because excess of oxygen content promotes the existence of rhombohedral phase [10]. Actually, after annealing under conditions resulting in stoichiometric oxygen content [8,10,11], this manganite became orthorhombic with v 59.29 Å 3 . The result obtained made it possible to find index γ 0.018 for aged manganite (Table I).…”

“…Since manganites, as well as ferrites, are oxide phases of variable composition containing ions of variable valency, great number of point defects, dislocations, and interacting with the surrounding atmosphere, there are common mechanisms and regularities of ageing processes in these groups of materials related to the thermodynamics and kinetics of solid-phase reactions [8][9][10]. General cause of the ageing is the lack of a true thermodynamic equilibrium under specified conditions.…”