Study of YBaCuO quasi-two-dimensional crystalline structure by light scattering

The following is a study of light scattering by C-oscillations of the apical oxygen O(4) ion, which has a specific role since the superconductive pairing mechanism is due to the fluctuation of O(4) positions in YBa2Cu3O7−x-type crystals. The schema for estimation of the apex oxygen content and a number of consequences resulting from the mixing of the electromagnetic g- and u-modes in a YBa2Cu3O7−x quasi-two-dimensional layer has been obtained. When oxygen vacancies are in the O(4)–Cu(1)–O(4) bridges (or another distortion of lattice symmetry), the C-vibrations of O(4) result in initiation of a dipole moment. At the same time they are associated with the Cu(1)–O(4) bond deformation. The latter one causes Raman scattering by dipole-active O(4)–oscillations. In the framework of the anharmonic oscillator model we have obtained the intensity of the second harmonic scattered signal, and sum and difference frequencies generated by YBa2Cu3O7−x nano-crystalline film as well.