  Electron paramagnetic resonance experiments on doped Yb3+ ions in YBaCuO
compounds with different oxygen contents have been made. We have observed the
strong temperature dependence of the EPR linewidth in the all investigated
samples caused by the Raman processes of spin-lattice relaxation. The
spin-lattice relaxation rate anomaly revealed near TC in the superconducting
species can be assigned to the phonon density spectrum changes
