63,65Cu nuclear quadrupole resonance study of Ni-doped YBa2Cu3O7

We have prepared pure YBCO (YBa 2 Cu 3 O 7− δ ) and Ni-doped YBCO (YBa 2− x La x Cu 3− x Ni x O 7− δ , x =0.1) samples and performed 63,65 Cu nuclear quadrupole resonance (NQR) measurements. La substitution introduced for charge compensation, as well as Ni doping, severely distorts the electric field gradient at the copper sites inducing extra 63,65 Cu NQR peaks other than the main peaks, for both the plane and the chain sites. 63,65 Cu NQR linewidths for the plane site increased significantly whereas those for the chain site remained similar. Furthermore, both the spin–lattice and the spin–spin relaxation times for the plane copper decreased whereas those for the chain copper increased. The Ni substitutional effects on linewidths and relaxation times confirm that Ni carrying a local moment substitutes for the plane copper.