Parameters of the electric-field gradient tensor at the copper sites in YBa2Cu3O7−y. Problems of comparison of calculated and experimental values

Mossbauer emission spectroscopy of the 67 Cu( 67 Zn) and 123 Ba( 133 Cs) isotopes was used to determine the parameters of the electric-field gradient (EFG) tensor of the 67 Zn 2+ centers at the Cu(1) and Cu(2) positions and of the 133 Cs + centers at the Ba positions in the lattices of YBa 2 Cu 3 O 7 and YBa 2 Cu 3 O 6 . A disagreement between the experimental values of the principal component of the EFG tensor with those calculated using the model of point charges prevented identification of charges carried by the lattice atoms. However, a comparison of the experimental and calculated values for YBa 2 Cu 3 O 7 makes it possible to determine the relative charges of the atoms and to identify the most probable structural formula of this compound