The substitution of non-magnetic Zn and magnetic Ni for Cu in the supercond
ucting CuO2 plane leads to a rapid decline in T-c and localised behaviour n
ear the impurities. There is no consensus about the mechanism for the supre
ssion of superconductivity or the origin of the localized behaviour. Some d
iscussion of these subjects is given based on NMR and NQR measurements. (C)
2000 Published by Elsevier Science B.V. All rights reserved.