Thermal properties of the Nd1−xCaxBaCo2O5.5 compositions (0 ≤ x ≤ 0.2)

Maria Gutowska , Jarosław Więckowski , Andrzej Szewczyk , Stanisław Koleśnik , Bogdan Dąbrowski , Maciej Kowalczyk , Jarosław Piętosa , Nedelko Natalia , Roman Minikayev

Abstract

Layered cobaltites RBaCo2O5.5, considered for application as cathodes of fuel cells, exhibit a rich spectrum of magnetic and electronic properties. Taking advantage of the fact that Nd3+ and Ca2+ ions have nearly identical ionic radii, by synthesizing the Nd1−xCaxBaCo2O5.5 compounds (for x = 0, 0.02, 0.06, 0.08, 0.16, and 0.2), a hole doping was realized, without significant disturbing the crystalline structure and the ordering of oxygen vacancies. In order to study the influence of the hole doping on thermal properties of these compositions, specific heat studies were performed over the temperature range from 2 to 395 K. The main, i.e., lattice, magnon and Schottky, contributions to the specific heat were separated from the total specific heat measured and described theoretically. In particular, the lattice contribution was described by combining the Debye and the Einstein models, whereas the magnon specific heat was described in frames of a model developed for anisotropic magnetic materials (A. I. Akhiezer et al., Sov. Phys. Usp. 3 (1961) 567). Changes of width and height of a specific heat anomaly accompanying the insulator-metal phase transition, appearing unmonotonously as a function of x, were ascribed to small deviations of the oxygen content from the assumed stoichiometry and to non-uniformity of the oxygen content over the sample volume. Smearing of specific heat anomalies related to magnetic phase transitions was found and attributed tentatively to disorder introduced by nonuniform distribution of the calcium ions within (Nd,Ca)–O planes. An impact of the calcium substitution on the position of the Schottky anomaly, related to thermal excitations of the Nd3+ ions, was found and interpreted qualitatively as a side effect of the hole doping, which causes also deformations of the crystalline structure and affects the magnetic structure of the Co sublattice.
Author Maria Gutowska - Instytut Fizyki Polskiej Akademii Nauk (Instytut Fizyki Polskiej Akademii Nauk)
Maria Gutowska,,
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, Jarosław Więckowski - Instytut Fizyki Polskiej Akademii Nauk (Instytut Fizyki Polskiej Akademii Nauk)
Jarosław Więckowski,,
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, Andrzej Szewczyk - Instytut Fizyki Polskiej Akademii Nauk (Instytut Fizyki Polskiej Akademii Nauk)
Andrzej Szewczyk,,
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, Stanisław Koleśnik - Northern Illinois University, Department of Physics, DeKalb
Stanisław Koleśnik,,
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, Bogdan Dąbrowski - Northern Illinois University, Department of Physics, DeKalb
Bogdan Dąbrowski,,
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, Maciej Kowalczyk ZMKF
Maciej Kowalczyk,,
- Division of Construction and Functional Materials
, Jarosław Piętosa - Instytut Fizyki Polskiej Akademii Nauk (Instytut Fizyki Polskiej Akademii Nauk)
Jarosław Piętosa,,
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, Nedelko Natalia - Instytut Fizyki Polskiej Akademii Nauk (Instytut Fizyki Polskiej Akademii Nauk)
Nedelko Natalia,,
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, Roman Minikayev - Instytut Fizyki Polskiej Akademii Nauk (Instytut Fizyki Polskiej Akademii Nauk)
Roman Minikayev,,
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Journal seriesJournal of Alloys and Compounds, ISSN 0925-8388
Issue year2016
Vol670
Pages175-181
Publication size in sheets0.5
Keywords in EnglishFuel cells; Heat capacity; Magnetically ordered materials; Oxide materials; Phase diagrams; Phase transitions
DOIDOI:10.1016/j.jallcom.2016.01.257
Languageen angielski
Score (nominal)35
ScoreMinisterial score = 35.0, 28-11-2017, ArticleFromJournal
Ministerial score (2013-2016) = 35.0, 28-11-2017, ArticleFromJournal
Publication indicators WoS Impact Factor: 2016 = 3.133 (2) - 2016=2.919 (5)
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