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Relating defect chemistry and electronic transport in the double perovskite Ba1−xGd0.8La0.2+xCo2O6−δ (BGLC)

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Abstract

Rare earth double perovskites comprise a class of functional oxides with interesting physiochemical properties both for low- and high-temperature applications. However, little can be found relating electrical properties with equilibrium thermodynamics of non-stoichiometry and defects. In the present work, a comprehensive and generally applicable defect chemical model is developed to form the link between the defect chemistry and electronic structure of partially substituted BGLC (Ba1−xGd0.8La0.2+xCo2O6−δ, 0 ≤ x ≤ 0.5). The equilibrium oxygen content of 4 different compositions is determined as a function of pO2 and temperature by thermogravimetric analysis, and combined with defect chemical modelling to obtain defect concentrations and thermodynamic parameters. Oxidation enthalpies determined by TG-DSC become increasingly exothermic (−50 to −120 kJ mol−1) with increased temperature and oxygen non-stoichiometry for all compositions, in excellent agreement with the thermodynamic parameters obtained from the defect chemical model. All compositions display high electrical conductivities (500 to 1000 S cm−1) with shallow pO2-dependencies and small and positive Seebeck coefficients (3 to 15 μV K−1), indicating high degree of degeneracy of the electronic charge carriers. The complex electrical properties of BGLC at elevated temperatures is rationalized by a two-band conduction model where highly mobile p-type charge carriers are transported within the valence band, whereas less mobile “n-type” charge carriers are located in narrow Co 3d band.

Graphical abstract: Relating defect chemistry and electronic transport in the double perovskite Ba1−xGd0.8La0.2+xCo2O6−δ (BGLC)

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Publication details

The article was received on 27 Mar 2017, accepted on 12 Jul 2017 and first published on 13 Jul 2017


Article type: Paper
DOI: 10.1039/C7TA02659E
Citation: J. Mater. Chem. A, 2017, Advance Article
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    Relating defect chemistry and electronic transport in the double perovskite Ba1−xGd0.8La0.2+xCo2O6−δ (BGLC)

    E. Vøllestad, M. Schrade, J. Segalini, R. Strandbakke and T. Norby, J. Mater. Chem. A, 2017, Advance Article , DOI: 10.1039/C7TA02659E

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