${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ and ${}_{}{}^{65}{}_{}{}^{}\mathrm{Cu}$ nuclear-quadrupole-resonance spectra of a series of materials of composition (${\mathrm{Y}}_{1\mathrm{-}\mathit{y}}$${\mathrm{Ca}}_{\mathit{y}}$)${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6+\mathrm{\delta }}$ with 0<y<0.5 and δ≪1 are reported. For y>0.1 these materials are superconducting with $T_c$ around 45 K. For y values below 0.25 the spectra consist of two components. One signal is identical to that of Cu(1) in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_6$, showing that the chain sites are not affected by the hole doping that accompanies substitution of Ca for Y. The other signal, which can be assigned to Cu(2) sites, is identical for all superconducting samples in the series and is not observed when y<0.1. Relaxation times indicate that the Cu(1) nuclei are in insulating environments, while the Cu(2) sites are conducting. Thus the conductivity is highly anisotropic. This is also demonstrated by far-infrared reflectance spectra. As Ca is added to ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_6$, there is a gradual decrease in the strength of the $E_u$ (ab plane) modes due to free-carrier screening. The $A_{2u}$ (c-axis) modes, on the other hand, remain unscreened at low frequencies.

• Received 24 April 1989

DOI:https://doi.org/10.1103/PhysRevB.40.8878