EPR study of vanadium-containing amorphous silica formed by sol–gel method

摘要: Abstract Spectra of electron paramagnetic resonance (EPR) sol–gel derived silica glass doped with vanadium (1 wt%) were measured at ∼9 GHz and ∼300 K after various stages the process (sol → fresh gel → aged gel → heat treated gel → glass). We show that source spectra solution aqua-complexes vanadyl resides in gel pores heat treatment temperatures T t ⩽973 K. The number ions a sample decreases increasing remainder is immobilized on pore surface local environments which species becomes undetectable. In temperature range collapse symmetrically shaped single component observed g  ∼ 1.96 attributed to V 4+ clusters. After ⩾1023 width this line increases above 340 assumed due formation crystalline inclusions non-stoichiometric VO 2 for insulator–metal transition commonly ∼340 volume phase less than detection limit X-ray diffraction technique used present work. For samples >1073 spectrum hyperfine structure (HFS) isolated tetrahedral coordination appears 77 parameters spin Hamiltonian orthorhombic symmetry indicate wave function ground state |3 z − r 〉 type. absorption bands maxima ∼770 ∼930 nm are optical these samples.