X-ray diffraction study of superstructure in GdBaCo{sub 2}O{sub 5.5}

A single crystal of GdBaCo{sub 2}O{sub 5.47(2)} has been studied by means of x-ray diffraction. Below the first-order metal-insulator transition, a continuous transition to a phase with a doubled orthorhombic unit cell is discovered at T{sub C}=341.5(7) by the appearance of very weak superstructure...

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Bibliographic Details
Published in:Physical review. B, Condensed matter and materials physics Condensed matter and materials physics, 2005-05, Vol.71 (18)
Main Authors: Chernenkov, Yu.P., Plakhty, V.P., Fedorov, V.I., Barilo, S.N., Shiryaev, S.V., Bychkov, G.L.
Format: Article
Language:English
Subjects:
ATOMIC DISPLACEMENTS
BARIUM COMPOUNDS
COBALT IONS
COBALT OXIDES
CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
DISTANCE
GADOLINIUM COMPOUNDS
ISING MODEL
LIGANDS
MONOCRYSTALS
ORDER PARAMETERS
ORDER-DISORDER TRANSFORMATIONS
ORTHORHOMBIC LATTICES
REFLECTION
SPIN
SYMMETRY
X-RAY DIFFRACTION
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Summary:A single crystal of GdBaCo{sub 2}O{sub 5.47(2)} has been studied by means of x-ray diffraction. Below the first-order metal-insulator transition, a continuous transition to a phase with a doubled orthorhombic unit cell is discovered at T{sub C}=341.5(7) by the appearance of very weak superstructure reflections. The critical exponent for the order parameter is found to be {beta}=0.328(8), indicating an Ising pseudospin ordering in a 3D system. The systematic extinction of the superstructure reflections evidences the crystal symmetry change from Pmmm to Pmma, which explains the existence of a spontaneous moment. The integrated intensities are used to calculate the atomic displacements from their positions in the high-temperature phase. The cobalt-ligand distances in the ordered phase are discussed in terms of possible spin-state and/or orbital ordering of Co{sup 3+} ions.
ISSN:1098-0121
1550-235X
DOI:10.1103/PhysRevB.71.184105