FLUCTUATIONS OF THE LOCAL MAGNETIC-FIELDS ON IMPURITY ER3-EARTH IONS IN YBA2CU3O6.85 SUPERCONDUCTOR( AND YB3+ RARE)

The Er3+ and Yb3+ EPR behavior is studied in oriented Y0,99(Er,Yb)0,01 Ba2Cu3O6,85 superconductors at low temperatures (T < T(c) = 85 K). Rar e earth ions are shown to be affected by the fluctuating almost-equal- to 160 Oe molecular copper ion field independent of the type of rare e arth ion, and directed Predominantly along the crystallographic c axis . For T > 6 K the rate or the field fluctuations increases with temper ature as an exponential law of W = 3,5.10(10) exp (-25/T). From the me asured dependence of the EPR Yb3+ line intensity on oxygen content in (Y,Yb)Ba2Cu3Ox and involving the experimental data on the Meissner eff ect and calculated probabilities for the formation of ortoI structural clusters on YBa2Cu3Ox, we conclude that observed EPR Er3+ and Yb3+ si gnals and dynamic effects in YBa2Cu3O6,85 characterize nonsuperconduct ing orthoIII phase occurring as layers or droplets between grains or s uperconducting orthoI phase in a noticeable (almost-equal-to 30% volum e) amount.