Synthesis, crystal structure and electrical properties of A-site cation ordered BaErMn{sub 2}O{sub 5} and BaErMn{sub 2}O{sub 6}
- AGH University of Science and Technology, Faculty of Energy and Fuels, Department of Hydrogen Energy, al. A. Mickiewicza 30, 30-059 Krakow (Poland)
- Department of Physics, Northern Illinois University, DeKalb, Illinois 60115 (United States)
In this paper, we report on a synthesis procedure, structural and electrical properties of BaErMn{sub 2}O{sub 5} and BaErMn{sub 2}O{sub 6}, A-site double perovskites having layered arrangement of Ba and Er cations. These materials belong to a family of BaLnMn{sub 2}O{sub 5+δ} oxides, which up to now were successfully synthesized for Ln=Y and La–Ho lanthanides. Up to our knowledge, this is the first report on the successful synthesis of BaErMn{sub 2}O{sub 5} and BaErMn{sub 2}O{sub 6}, yielding>95 wt% of the considered compounds. Structural characterization of the materials is given at room temperature, together with in situ XRD studies, performed during oxidation of BaErMn{sub 2}O{sub 5} in air, at elevated temperatures up to 500 °C. A complex structural behavior was observed, with oxidation process of BaErMn{sub 2}O{sub 5} occurring at around 300 °C. The oxidized BaErMn{sub 2}O{sub 6} shows a structural phase transition at about 225 °C. Results of structural studies are supported by thermogravimetric measurements of the oxidation process, performed in air, as well as reduction process, preformed in 5 vol% of H{sub 2} in Ar. Additionally, isothermal oxidation/reduction cycles were measured at 500 °C, showing interesting properties of BaErMn{sub 2}O{sub 5+δ}, from a point of view of oxygen storage technology. Electrical conductivity of BaErMn{sub 2}O{sub 5} is of the order of 10{sup −4} S cm{sup −1} at room temperature and shows activated character on temperature with activation energy E{sub a}=0.30(1) eV. Positive sign of Seebeck coefficient for this material indicates holes as dominant charge carriers. Oxidized BaErMn{sub 2}O{sub 6} possesses much higher electrical conductivity, almost 0.2 S cm{sup −1} at room temperature. Additional, about 10-fold increase of electrical conductivity, occurring in the vicinity of 225 °C for this material, can be associated with phase transition from charge/orbital-ordered insulator COI(CE) to paramagnetic metal PM phase. The highest conductivity for BaErMn{sub 2}O{sub 6} was measured near 500 °C and is almost equal to 40 S cm{sup −1}, while negative sign of Seebeck coefficient can be associated with electrons being dominant charge carriers. - Graphical abstract: Structure and oxygen storage properties of BaErMn{sub 2}O{sub 5+δ}. - Highlights: • Synthesis of BaErMn{sub 2}O{sub 5} and BaErMn{sub 2}O{sub 6}. • Structural and transport properties of BaErMn{sub 2}O{sub 5+δ}. • Oxygen storage in BaErMn{sub 2}O{sub 5}–BaErMn{sub 2}O{sub 6} system. • Phase transitions in BaErMn{sub 2}O{sub 6}.
- OSTI ID:
- 22309018
- Journal Information:
- Journal of Solid State Chemistry, Vol. 203; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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