Square planar coordination, high cuprates

The crystal structure of high (90 K) superconducting cuprates is based on a perovskite lattice with an orthorohonibic distortion [124] (Figure 5.28). In the various families of the.se compounds, copper ions exhibit various coordinations four planar-square, five pyramidal, six octahedral. In all cases the four bonds in the perovskite layers are shorter that the Cu-0 bonds between layers. 

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