Effect of cationic order?disorder on the transport properties of LaBaCo2O6?d and La0.5Ba0.5CoO3?d perovskites

D. GARCÉS; C. MARTINEZ SETEVICH; A. CANEIRO; G. CUELLO

JOURNAL OF APPLIED CRYSTALLOGRAPHY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2014 vol. 47 p. 325 - 334

0021-8898

A-site cationic ordered LaBaCo2O6 and disordered La0.5Ba0.5CoO3perovskite phases were obtained by solid state reaction. Their structuralproperties were studied at room temperature and 673 K, by combining powderdiffraction techniques, X-ray diffraction and neutron powder diffraction with anindependent determination of the oxygen content of the samples bythermogravimetry. La0.5Ba0.5CoO3 exhibits cubic symmetry with cationsrandomly distributed, whereas LaBaCo2O6 shows tetragonal symmetry withthe La3+ and Ba2+ ions distributed in alternating layers. The diffraction datawere analyzed using the Rietveld method and different structural andmicrostructural models. Bond valence and Fourier methods were used todetermine bond distances and neutron/electron density maps. LaBaCo2O6exhibits a higher concentration of oxygen vacancies than La0.5Ba0.5CoO3,because the O atom is weakly bonded to the LaO layers. The anisotropic atomicdisplacement and the neutron density distribution suggest a two-dimensionalO-migration path for LaBaCo2O6 and a three-dimensional path forLa0.5Ba0.5CoO3.The mechanism of electrical conductivity is via electron holeswith high mobilities (La0.5Ba0.5CoO3 = 2.49 cm2 V1 s1 and LaBaCo2O6 =1.48 cm2 V1 s1 at room temperature) and low activation energy (EaLaBaCo2O6 =0.019 eV and EaLa0.5Ba0.5CoO3 = 0.030 eV). It has also been found that the higherelectronic and ionic conductivities in La0.5Ba0.5CoO3 compared to those inLaBaCo2O6 are due to the higher dimensionality of transport and to greateroverlapping between the Co 3d and O 2p orbitals.