Oxygen-vacancy ordering in the YBa2Cu3Oz basal plane studied by the cluster variation method |
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| Authors: | A. Berera L. T. Wille D. de Fontaine |
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| Affiliation: | (1) Materials and Chemical Sciences Division, Lawrence Berkeley Laboratory, 94720 Berkeley, California;(2) Department of Physics, University of California, 94720 Berkeley, California;(3) Department of Materials Science and Mineral Engineering, University of California, 94720 Berkeley, California |
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| Abstract: | The cluster variation method is used to calculate a phase diagram for a two-dimensional Ising model representing the Cu2O plane of the high-Tc superconductor YBa2Cu3Oz. Both first (V1 and second-neighbor (V2) interactions are considered, withV2/V1= –1/2; At high temperatures, the transition from the disordered (tetragonal) to the ordered (orthorhombic) phase is second-order. A tricritical point is found below which phase separation occurs. Fractional site occupancy and second-neighbor pair correlations are calculated as a function of temperature. The relevance of the model to the thermodynamics of ordering in the high-Tc compound is discussed. |
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| Keywords: | Two-dimensional Ising model cluster variation method superconductors |
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