Use of isotropic substitution for establishing the vibrational spectrum of copper atoms in YBa2Cu3O7-x

For two specimens of the superconducting YBa2Cu3O7-y compound produced out of the natural copper isotopes mixture and out of the mixture of copper-65 isotopes enriched up to 99 at% the thermal vibration spectra have been measured by neutron inelastic scattering. The neutron scattering cross-section for the first mixture was almost two times less than for the second one. The thermal vibration spectrum of the copper atoms for YBa2Cu3O7-y has been established from the experimental data. It is shown that the energy of the copper atoms vibrations spreads up to 40 MeV