We report 63,65 Cu nuclear quadrupole resonance ͑NQR͒ spectra of Sr-substituted Y(Ba 1Ϫx Sr x ) 2 Cu 3 O 7Ϫ␦ at room temperature. The chemical pressure effect associated with Sr substitution leads to the results that the planar Cu͑2͒ NQR signals are shifted to higher frequencies and the chain Cu͑1͒ NQR signals are shifted to lower frequencies. With Sr substitution, the 63,65 Cu NQR linewidths increase significantly for both the Cu͑2͒ plane site and Cu͑1͒ chain site, and a new Cu NQR peak appears, which we expect, originates from partial oxygen disorder in the CuO x chain layers. We expect that T c reduction with Sr substitution in Y123 is due to carrier inhomogeneous distribution and localization caused by the partial oxygen disorder in the CuO x chain layers, or the suppression of the resonant tunneling between the CuO 2 planes.

The effect of substitution of Pr for Sm on the Cu NQR spectra of Sm1−xPrxBa2Cu3O7−y is observed. The decrease of the NQR peak positions with increasing Pr concentration displays the influence of Pr atoms which modify the quadrupole interaction at the Cu(2) sites. This demonstrates that Pr doping changes the electric charge distribution in the vicinity of the Cu(2) sites. It provides information on the normal‐state properties of high‐Tc superconductors.