Electron spin resonance of Gd3+ in glasses of the soda-silica-yttria system

Abstract

The electron spin resonance of the Gd³⁺ ion has been studied in two series of glasses having the molar compositions 6SiO₂:5Na₂O: x (Gd₂O₃ + Y₂O₃) with 0 ≤ x ≤ 0.5 and 500SiO₂: x Na₂O:1Gd₂O₃ with 2.5 ≤ x ≤ 494. The spectra were nearly independent of temperature and sample composition, but varied strongly with microwave frequency in the range 5.4–38.4 GHz. The data were interpreted in terms of the spin Hamiltonian for a strong cubic crystal field and also in terms of the usual rhombic spin Hamiltonian $\mathcal{H}{\mathrm{=\; g\hspace{0.17em}}}_0\beta \mathbf{H}·\mathbf{S}{\mathrm{+\; D[S}}_z^2{\text{− (1/3)S \hspace{0.17em}(S + 1)] + E(S}}_x^2{\mathrm{-\; S}}_y^2)$ with S = (7/2). Computer calculations were made yielding all possible effective g values for this latter Hamiltonian for all physically distinct combinations of the crystal field parameters when the Zeeman field H was restricted to the x, y, or z direction. The resonance features were related to three distinct sites for the Gd³⁺ ion. The spectra are indicative of a chemically heterogeneous glass matrix composed of soda‐rich, silica‐rich, and diffuse transition regions. The heterogeneities were found to exist over the entire range of compositions studied. Variations in the resonance intensity associated with the soda‐rich region suggest the existence of a very well‐defined substructure within the region. The data indicate that the substructure is related to the fundamental structural features of the possible crystalline compounds which can exist within the composition range.