Fizika Nizkikh Temperatur: Volume 43, Number 9 (September 2017), p. 1342-1353    ( to contents , go back )

Influence of K+ ions and superstoichiometric manganese on structure defects, magneto-transport and dielectric properties of magnetoresistance La0.7Ca0.3–xKxMn1+xO3–δ ceramics

N.A. Liedienov1, A.V. Pashchenko1,2, V.P. Pashchenko1, V.K. Prokopenko1, D.D. Tatarchuk3, Yu.F. Revenko1

V.A. Turchenko1,4, V.V. Burchovetskii1, V.Ya. Sycheva1, A.G. Sil’cheva1, Yu.V. Didenko3, and G.G. Levchenko1

1O. Galkin Donetsk Institute for Physics and Engineering of the National Academy of Sciences of Ukraine 46 Nauky Ave., Kyiv 03680, Ukraine

2Донецкий национальный университет экономики и торговли им. М. Туган-Барановского, г. Кривой Рог, 50005,Украина
E-mail: alpash@mail.ru

3National Technical University of Ukraine “KPI”, 37 Peremogy Ave., Kiev 03056, Ukraine

4Joint Institute for Nuclear Research, Dubna 141980, Russia

Received November 24, 2016, revised February 14, 2017

Abstract

Structure, its defectiveness, nanostructural clustering and functional properties of La0.7Ca0.3–xKxMn1+xO3–δ ceramics with x = 0–0.3 have been investigated by x-ray diffraction, thermogravimetric, SEM, resistance, magnetic, magnetoresistance and dielectric spectroscopy methods. It was established that lattice parameter of cubic structure increases when ions of Ca2+ are substituted by K+ ones. It has been shown that a real perovskite structure contains variable valence state of manganese MnA2+, MnB3+ and MnB4+ in A- and B-positions as well as point defects of vacancy type, which are anionic V(a) and cationic V(c) vacancies. The increase in content of superstoichiometric manganese is connected to the nanostructured clustering process. It was found out that K+ and superstoichiometric manganese cause the increase in relative permittivity ε' and dielectric loss tangent tan δ. The experimental phase diagram of magnetic state has been constructed. It allows to determine composition of the magneto-resistance La0.7Ca0.3–xKxMn1+xO3–δ ceramics with desirable magnetotransport properties. The optimal La0.7Ca0.3–xKxMn1+xO3–δ composition with the high-est magnetoresistance effect at the room temperature has been determined by the comparing functional properties of lanthanum-calcium, lanthanum-stron-tium and lanthanum-calcium-potassium manganites.

PACS: 61.72.–y Defects and impurities in crystals; microstructure;
PACS: 75.47.–m Magnetotransport phenomena; materials for magnetotransport;
PACS: 75.47.Gk Colossal magnetoresistance;
PACS: 77.22.Ch Permittivity (dielectric function).

Key words: manganites, defectiveness, dielectric properties, phase transitions, magnetoresistance effect.

Published online:: July 25, 2017

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