Electron paramagnetic resonance of V4+ ions in lanthanum-aluminosilicate glasses

The EPR and optical absorption spectra of V 4+ ions and their relation with the structural features of glasses in the system La 2 O 3 - Al 2 O 3 - SiO 2 are investigated. Three characteristic ranges of the V 4+ EPR parameters are established: I) A ∥ ≈ 167 × 10 -4 cm -1 , g ∥ = 1.937 - 1.938; II) A ∥ ≈ (163 - 164) × 10 -4 cm -1 , g ∥ = 1.939 - 1.940; III) A ∥ ≈ (156 - 159) × 10 -4 cm -1 , g ∥ = 1.945. It is shown that in the region I with low La 2 O 3 content the lanthanum is predominately a modifying ion, and in glass with a high La 2 O 3 concentration lanthanum gradually occupies a site in the glass, bonding silicon-oxygen and aluminum-oxygen tetrahedra, i.e., it becomes a glass former even though its ionic radius is large. Region III glasses with high La 2 O 3 content possess a high softening temperature and anomalously high thermal conductivity (about 12.6 W/(m ∙ K)).