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

The EPR and optical absorption spectra of V⁴⁺ ions and their relation with the structural features of glasses in the system La₂O₃ – Al₂O₃ – SiO₂ are investigated. Three characteristic ranges of the V⁴⁺ 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 La₂O₃ content the lanthanum is predominately a modifying ion, and in glass with a high La₂O₃ 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 La₂O₃ content possess a high softening temperature and anomalously high thermal conductivity (about 12.6 W/(m ∙ K)).