Structural investigations of V _2O _5-P _2O _5-CaO glass system by FT-IR and EPR spectroscopies

摘要

xV _2O _5?(100 - x)[0.7P _2O _5?0.3CaO] glass system was obtained for 0 ≥ x ≥ 35 mol% V _2O _5. In order to obtain information regarding their structure, several techniques such as X-Ray diffraction, FT-IR, and EPR spectroscopies were used. X-Ray diffraction patterns of investigated samples are characteristic of vitreous solids. FT-IR spectra of 0.7P _2O _5?0.3CaO glass matrix and its deconvolution show the presence in the glass structure of all structural units characteristic to P _2O _5. Their number are increasing for x ≥ 3 mol% V _2O _5 then, for higher content of vanadium ions, the number of phosphate structural units are decreasing leading to a depolymerization of the structure. The structural units characteristic to V _2O _5 were not evidenced but their contribution to the glass structure can be clearly observed. EPR revealed a well resolved hyperfine structure (hfs) typical for vanadyl ions in a C _(4v) symmetry for x ≥ 3 mol% V _2O _5. For 5 < x < 20 mol% V _2O _5 the spectra show a superposition of two EPR signals one due to a hfs structure and another consisting of a broad line typical for associated V ~(4+)-V ~(4+) ions. For x ≥ 20 mol% V _2O _5 only the broad line can be observed. The composition dependence of the line-width suggests the presence of dipole-dipole interaction between vanadium ions up to x ≥ 5 mol% V _2O _5 and superexchange interactions between vanadium ions for x > 5 mol% V _2O _5.