Thermal Expansion and Symmetry of YBa sub 2 Cu sub 3 O sub 7

Yttrium--barium--copper-oxide (YBC)-single crystals have been investigated by X-ray methods in the temperature range from 30-300K. A small anomaly of the lattice deformation has been found at the transition temperature T sub c , along b, the direction of the Cu--O--Cu-chains. For the a- and c-direct...

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Bibliographic Details
Published in:Journal of the less-common metals 1990-05, Vol.164-165 (1-2), p.146-151
Main Authors: Dernbach, D, Ehses, K H
Format: Article
Language:English
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Summary:Yttrium--barium--copper-oxide (YBC)-single crystals have been investigated by X-ray methods in the temperature range from 30-300K. A small anomaly of the lattice deformation has been found at the transition temperature T sub c , along b, the direction of the Cu--O--Cu-chains. For the a- and c-directions, no effect could be detected. The thermal expansion coefficient does not jump at T sub c , as expected for a second order phase transition. However, d alpha /dT is discontinuous at T sub c . This behaviour indicates no direct correlation between structural effects and superconductivity. The temperature dependence of the spontaneous deformation can be described by an "extrinsic" order parameter. It is coupled to an "intrinsic" one, which is responsible for the onset of superconductivity. A group theoretical discussion of the symmetry of both order parameters requires knowledge of the space groups. Measurements of Bijvoet-differences suggest the space group Pmm2 instead of Pmmm for the room temperature phase. Graphs. 10 ref.--AA
ISSN:0022-5088