The dimpling in the CuO2 planes of YBa2Cu3Ox (x=6.806-6.954, T=20-300K) measured by yttrium EXAFS

The dimpling of the CuO2 planes (spacing between the O2,3 and Cu2 layers) i n YBa2Cu3Ox has been measured as a function of oxygen concentration and tem perature by yttrium X-ray extended-fine-structure spectroscopy (EXAFS). The relative variations of the dimpling with doping (x = 6.806-6.984) and temp erature (20-300K) are weal; (within 0.05 Angstrom), and arise mainly from d isplacements of the Cu2 atoms off the O2,3 plane towards Ba. The dimpling a ppears to be connected with the transition from the underdoped to overdoped regimes at x = 6.95, and with a characteristic temperature in the normal s tate, T* similar or equal to 150K. (C) 1998 Elsevier Science Ltd. All right s reserved.