The Effect of γ Irradiation on Phase Transitions in the Polyimide–YBa₂Cu₃O_{6 + x} System

Abstract

The effect of γ irradiation on optical properties of films of the polyimide–YBa₂Cu₃O_6.7 system with different concentrations of the filler in the form of the finely crystalline compound YBa₂Cu₃O_6.7 (0.05 wt %, 0.10 wt %, and 0.50 wt %) has been investigated. The properties were studied on an IKS-29 infrared spectrophotometer in a spectral range of 400–4200 cm^–1 at room temperature. The samples were irradiated in air under room conditions on an RKhM-γ-20 by doses of 150, 250, and 600 kGy. The power of the exposure dose of the ⁶⁰Co source was 0.16 rad/s. It has been established that irradiation with a dose of up to 600 kGy of the abovementioned system slightly affects the structure of the polyimide matrix but decreases the number of free radical groups in the film structure with the formation of hydrogen bonds. In the range of 400–4200 cm^–1 at D = 150 kGy, the most intense changes in spectra of polymeric composite samples have been revealed. In the range of 2850–3350 cm^–1, the wide absorption spectrum band is preserved, which is caused by the presence of Cu, Y, and Ba crystallohydrates. The band is related to deformation vibrations of the Cu–O bond in YBa₂- Cu₃O_6.7 (YBCO) chains due to properties of barium carbonate, formation of oxygen vacancies in the filler, and vibrations of the Cu(I)–O(I) bonds near one or several O(4) vacancies. Irradiation by doses of 250 and 600 kGy for different concentrations of the filler leads to a decrease in the signal intensity in the range of 1800–3600 cm^–1 by 20–35% on average. Peaks related to interband transitions (transitions of the Cu(I)–Cu(IY)–Cu(II) system) and bending vibrations O(I)–Cu(I) are not changed by strains of O(IY)–Cu(I) bonds. This testifies to the radiation-stimulated diffusion of oxygen atoms to O(IY) sites determining the orthorhombic phase of YBa₂Cu₃O_6.7 from the occupied positions in the Cu–O sublattice.