Combined X-ray and Neutron Powder Diffraction Study on B-Site Cation Ordering in Complex Perovskite La2(Al1/2MgTa1/2)O6

Solids, vol. 4, pp. 87–93

Abstract

Complex perovskite La2(Al1/2MgTa1/2)O6 (LAMT) crystallizes in a monoclinic unit cell with space group P21/n at room temperature. Its B-site cations are ordered in a rock-salt-type arrangement. Previously, the full occupancy of Mg on the 2c-Wyckoff position was deduced from powder X-ray diffraction (PXRD). However, conventional X-rays could not properly resolve the mixed occupation on the B-site, since there is little scattering contrast between the neighbouring elements Mg and Al of the periodic table. Hence, complementary neutron diffraction studies were carried out to verify the exact B-site cation ordering in the unit cell. In this specific configuration of the B-cations, with its occupancy ratio and the presence of a heavy element Ta as well as neighbouring elements Mg and Al, only the strategy of a combined Rietveld analysis using both the X-ray and neutron diffraction data simultaneously succeeded in elucidating an accurate B-site cation ordering in this complex perovskite system. A full occupancy of Mg on the 2c-Wyckoff position and each a half occupancy of Al and Ta on the 2d-Wyckoff position could be resolved for the rock-salt-type ordering of the B-site cations in the monoclinic unit cell of LAMT.

Authors 5

1. Yoo Jung Sohn corresponding

   Forschungszentrum Jülich

   Affiliation as printed

   Institute of Energy and Climate Research, Materials Synthesis and Processing (IEK-1), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

2. Volodymyr V. Baran

   Deutsches Elektronen-Synchrotron DESY · Heinz Maier-Leibnitz Zentrum · Technical University of Munich

   Affiliation as printed

   Deutsches Elektronen-Synchrotron (DESY), Notkestraße 85, 22607 Hamburg, Germany

   Heinz Maier-Leibnitz Zentrum, TU München, 85747 Garching, Germany

3. Ralph Gilles

   Heinz Maier-Leibnitz Zentrum · Technical University of Munich

   Affiliation as printed

   Heinz Maier-Leibnitz Zentrum, TU München, 85747 Garching, Germany

4. Georg Roth Aachen Institute of Crystallography

   RWTH Aachen University

   Affiliation as printed

   Institute of Crystallography, RWTH Aachen University, 52066 Aachen, Germany

5. Robert Vaßen

   Forschungszentrum Jülich

   Affiliation as printed

   Institute of Energy and Climate Research, Materials Synthesis and Processing (IEK-1), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany