EFFECTS OF IMPURITIES ON THE INPLANE THERMAL-CONDUCTIVITY OF INSULATING YBA2CU3O6

We have measured the in-plane thermal conductivity K(T) for insulating single crystals of YBa2Cu3O6 doped with Er atoms in the Y site and Ni and Zn in the Cu(2) site. Thermal conductivity of pure YBa2Cu3O6 indi cates a significant additional heat resistance at temperatures near th e antiferromagnetic transition and below 200 K. Erbium impurities incr ease the phonon scattering, the effect being most pronounced at T < 15 0 K. The 3-d impurities strongly suppress the thermal conductivity at T > 15 K even for concentrations less than 2.5 at.%. The experimental data suggest that acoustic phonons are strongly coupled with spin exci tations in CuO2 planes.