Copper NQR study of the La 214 system from an aspect of microscopic environment of copper

The nuclear quadrupole resonance (NQR) has been investigated for Cu in La2−xA x CuO y (A=Sr and Ba). Three Cu NQR lines, A, B and C, have been observed, which correspond to three different Cu sites. From the analysis of these NQR intensities, site assignments are possibly as follows. These lines A, B and C are attributed to CuO6 octahedral, CuO5 pyramidal and CuO4 planar sites, respectively. The apical oxygen O(2) is induced to transfer to the interstitial O(3) site between LaO planes when two or more Sr2+ ions are located in its neighboring La sites. The excess holes doped into the CuO2 plane are provided mainly by O(3) as well as the unpaired Sr2+ ion.