INPLANE LATTICE EXPANSION ANOMALIES OF UNTWINNED SINGLE-CRYSTALS OF YBA2CU3O7-DELTA SUPERCONDUCTOR

The Anisotropic lattice expansion of untwinned single crystals of YBa2Cu3O7-delta was measured by a high resolution x-ray diffraction technique. Several slope discontinuities including ones near T(c) were observed. In comparison to the recent internal friction studies, it was found that every lattice expansion anomaly seen in a and b axes has a corresponding internal friction peak. In particular, the internal friction anomalies near T(c) is consistent with the Akhieser effect, indicating that the slope discontinuity and the internal friction anomaly have the same microscopic origin, i.e., lattice fluctuations.