Temperature-Dependent EXAFS Spectra of YBa 2 Cu 3 O 7-δ

We present EXAFS data on YBa 2 Cu 3 O 7-δ taken at four temperatures: 80 K, 112 K, 170 K, and 297 K. Spectra from both the Y edge and Cu edge are analyzed for the mean distances to near neighbors and the mean square relative displacements, σ 2 . The distances show small temperature dependences. The σ 2 's are unusal, decreasing more strongly at low temperature (112 K to 80 K) than at high temperature (300 K to 170 K). This could indicate some softening of the bond strengths and may indicate a phase transition.