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Synchrotron x-ray diffraction measurements on a high purity single crystal reveal that the absence of long-range ortho-II order in YBa&Cu306+, is most likely due to random-field effects. The ortho-II superstructure peaks show three qualitative features consistent with random-field behavior: First, instead of the development of a sharp Bragg peak at the transition Tot& = 125(5) 'C (for x = 0.5), the initial diffuse anisotropic Lorentzian (critical scattering) above Tp~, transforms to a Lorentzian-squared form below Tp». Second, the equilibration time increases dramatically at the onset of ordering. And third, the domain growth is logarithmic in time below Tp».

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