Effective Atomic Charges in YBa2Cu3O7 and La2-xSrxCuO4 Crystal Lattices
Experimental values of the electric field gradient tensor parameters (obtained by emission Mössbauer spectroscopy with the 57Fe, 67Zn, 155Gd isotopes, and by nuclear quadrupole resonance with the 17O and 137Ba nuclei) match with the calculated ones (point charge model) for the YBa2Cu3O7 and La2-xSrxCuO4 lattices of high-temperature superconductors only under the assumption that electronic defects are localized within chain and planar oxygen sublattices in YBa2Cu3O7 and within planar oxygen sublattice in La2-xSrxCuO4.