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Crystal structure, thermal expansion and high-temperature electrical conductivity of A-site deficient La2-zCo1+y(MgxNb1-x)(1-y)O-6 double perovskites
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
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Number of Authors: 8
2015 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 229, 243-251 p.Article in journal (Refereed) Published
Abstract [en]

New La-deficient double perovskites with P2(1)/n symmetry, La-similar to 1.90(Co1-x2+Mgx2+)(Co1/33+Nb2/35+)O-6 with x=0, 0.13 and 0.33, and La-2(Co1/22+Mg1/22+) (Co1/23+Nb1/25+)O-6 were prepared by solid state reaction at 1450 degrees C. Their crystal structures were refined using time-of-flight neutron powder diffraction data. Our results show that certain cations such as Nb5+, with very strong B-O bonds in the perovskite structure, can induce A-site vacancies in double perovskites. Upon heating in N-2 gas atmosphere at 1200 degrees C similar to 1% O atom vacancies are formed together with a partial reduction of the Co3+ content. The average thermal expansion coefficient between 25 and 900 degrees C of La-1.90(Co2/32+Mg1/32+)(Co1/33+Nb2/35+)O-6 was determined to be 17.4 ppm K-1. Four-point electronic conductivity measurements showed that the compounds are semiconductors, with conductivities varying between 3.7.10(-2) and 7.7.10(-2) S cm(-1) at 600 degrees C and activation energies between 0.77 and 0.81 eV. Partial replacement of La3+ with Sr2+ does not lead to any increase of conductivity, while replacement of Mg2+ with Cu2+ in La1.9CoCu1/3Nb2/3O6 and La1.8CoCu1/2Nb1/2O6 leads to similar to 100 times larger conductivities at 600 degrees C, 0.35 and 1.0 S cm(-1), respectively, and lower activation energies, 0.57 and 0.73 eV, respectively.

Place, publisher, year, edition, pages
2015. Vol. 229, 243-251 p.
Keyword [en]
Double perovskite, A-cation deficiency, Crystal structure, Neutron powder diffraction, Conductivity
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:su:diva-120173DOI: 10.1016/j.jssc.2015.06.009ISI: 000358815100031OAI: oai:DiVA.org:su-120173DiVA: diva2:851766
Available from: 2015-09-07 Created: 2015-09-02 Last updated: 2017-12-04Bibliographically approved

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Golod, TarasGrins, JekabsSvensson, Gunnar
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