Abstract
The effect of mechanical processing in different types of activators on the structure and physicochemical properties of the oxides LnMnO3+δ (Ln = Sm, Nd, La) has been studied. The optimal modes of mechanical activation for transformation the oxides under consideration to nanostructured state have been defined. Mechanical processing has been shown to cause a significant change of Jahn-Teller distortion parameters and temperatures of the cooperative Jahn-Teller phase transition. The presence of connection between redox processes and destruction of orbital ordering has been demonstrated. Very low values (10 -21 -10 -24 m 2 /s) of the oxygen bulk diffusion coefficient have been obtained for the oxides under consideration in the temperature range of 400 - 750°C. The diffusion activation energies are close to 1 eV, indicating the oxygen diffusion proceeds through structural defects at these temperatures.
Highlights
Rare Earth Manganites possess multiferroic effects, the colossal magnetoresistance and other unique properties [1, 2]
X-ray diffraction (XRD) analysis of the samples was performed on SHIMADZU diffractometer XRD-7000 using CuKα-radiation with a monochromator
In order to determine the effect of mechanical activation of oxides SmMnO3+δ and NdMnO3+δ on the cooperative Jahn-Teller phase transition, high temperature diffraction studies were carried out on the original samples and samples treated in the mill AGO-2 for 30 seconds
Summary
Rare Earth Manganites possess multiferroic effects, the colossal magnetoresistance and other unique properties [1, 2]. Due to heterovalent substitution of cations in doped manganites Ln1-xAxMnO3±δ (Ln= rare earth element, A = divalent metal cation, δ = oxygen non-stoichiometry), there is a variable oxidation degree of manganese, which is responsible for the appearance of the colossal magnetoresistance and other unique properties of these materials [12]. The substitution of La in the LaMnO3 manganite for another rare earth element (in particular, Ce, Pr, Nd, Sm, Gd) was shown to greatly affect the structure, thermodynamic stability, transport, electrical and magnetic properties [13,14,15]. Mechanical activation method for preparation of nanopowder materials became popular mainly for metal systems This method has been applied to manganites of rare earth elements in this work. Oxygen isotope exchange (OIE) study was carried out by nuclear microanalysis [21]
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