To the nuclear quadrupole resonance theory in YBa2Cu3O6+x

The values of the electrical field gradient (EFG) components on yttrium-barium ceramic ion nuclei depending on the oxygen content x are calculated. Comparison of calculation results to experimental data allows one to unambiquously ascertain the origin of different signals from nuclei in copper ion nodes. It is found that the main copper EFG tensor axis in a basis plane should change its direction with the change of x. The theory proceedes from the valent electron charge distribution obtained non-empirically, in the space and is not linked with the point ion model. It is shown that this model cannot serve as a basis for a reliable interpretation of nuclear quadrupole resonance (NQR) in the compounds considered