The local field distribution of in transition metal fluoride glasses investigated by electron paramagnetic resonance

Abstract

The EPR spectra of Gd 3+ in two transition metal fluoride glasses (PZG and PBI) have been extensively studied as functions of temperature, Gd 3+ concentration and microwave frequency (S, X, K and Q bands). The marked changes observed in the EPR spectra with temperature and concentration imply the existence of pairs of Gd 3+ ions. The spectra of isolated Gd 3+ ions were obtained at low temperature for samples with low Gd 3+ doping concentration. Isolated Gd 3+ ions are characterized by a fine-structure b 0 2 -parameter distribution within the range 0.02-0.15 cm −1 . The simulations of these spectra are computed with a Czjzek finestructure parameter distribution (this solution prohibits the existence of axial symmetry sites). It indicates a decrease of the number of geometrical constraints compared to those for Cr 3+ and Fe 3+ (octahedral coordination in a fluoride medium), in agreement with the higher Gd 3+ coordination numbers. Gd 3+ -ion sites are found to be more distorted in PZG than in PBI, suggesting that the glass network has an influence on the Gd 3+ polyhedron distortion amplitude.

β-Irradiation effects in Gd-doped borosilicate glasses studied by EPR and Raman spectroscopies

“…2, show well-known lines for socalled 'U' spectrum at 1173, 2460, and 3450 G (g $ 6.0, 2.8, and 2, respectively) typical for Gd 3+ ion in glasses with S = 7/2 [8,11]. The last asymmetric line at 1535 G (g $ 4.8) is attributed to another Gd 3+ site in glasses [11,15]. A broad line (6000 G width) around g $ 2 appears in the EPR spectrum and its intensity increases as a function of gadolinium oxide doping.…”

Structural and magnetic properties of lead-bismuthate oxide glasses containing S-state paramagnetic ions

“…The U type Gd 3þ -EPR spectrum is characteristic for Gd 3þ ions in structurally disordered systems. The lines from U spectrum with g % 5:9, 2.85 and 2.0 are assigned to Gd 3þ ions in sites with intermediate crystal fields having coordination numbers higher than 6, while the g % 4:8 line is characteristic for Gd 3þ ions in sites of strong crystal fields having a low coordination number [37]. Such incompletely coordinated species usually occur only at the surface of oxide systems [32].…”

MAS NMR spectra of quadrupolar nuclei in disordered solids: The Czjzek model

“…He thus defines the so-called degenerate model by empirically modifying the exponent of r in Eq. (6). Although the degenerate model, by introducing an empirical adjustable parameter (the exponent), might allow a better fit of the lineshape, this result would be obtained at the expense of the physical meaning of the PDF.…”

“…To be able to provide a structural interpretation of the NMR spectra of disordered materials, it is thus necessary to formulate a probability density function (PDF) to describe the distribution of the parameters defining the strength (t Q ) and shape (g) of the quadrupolar interaction tensor. This not so trivial problem of applied statistics (going from spatial, or electronic, disorder to a distribution of the EFG and finally to a distribution of quadrupolar parameters) was solved at the beginning of the eighties by Czjzek within the context of Mossbauer spectroscopy [2] and later successfully applied to Electron Spin Resonance and Perturbed Angular Correlations technique in glasses [3][4][5][6] and alloys [7,8]. It has been, however, only recently that several authors have advocated the use of the Czjzek model for the analysis of the magic angle spinning (MAS) NMR spectra of disordered materials, glasses [9][10][11][12] and spinel-type solids [13].…”