We report ${}^{63,65}\mathrm{Cu}$ nuclear quadrupole resonance (NQR) spectra of Sr-substituted $\mathrm{Y}({\mathrm{Ba}}_{1-x}{\mathrm{Sr}}_x{)}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ at room temperature. The chemical pressure effect associated with Sr substitution leads to the results that the planar Cu(2) NQR signals are shifted to higher frequencies and the chain Cu(1) NQR signals are shifted to lower frequencies. With Sr substitution, the ${}^{63,65}\mathrm{Cu}$ NQR linewidths increase significantly for both the Cu(2) plane site and Cu(1) chain site, and a new Cu NQR peak appears, which we expect, originates from partial oxygen disorder in the ${\mathrm{CuO}}_x$ 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 ${\mathrm{CuO}}_x$ chain layers, or the suppression of the resonant tunneling between the ${\mathrm{CuO}}_2$ planes.

• Received 8 January 2002

DOI:https://doi.org/10.1103/PhysRevB.66.012506