Electron paramagnetic resonance determination of the local field distribution acting on Cr³⁺and Fe³⁺in transition metal fluoride glasses (TMFG)

Abstract

Cr3+ and Fe3+ ions are used as paramagnetic probes of the local order in diamagnetic transition metal fluoride glasses (TMFG). EPR observations are made at S, X, K and Q band frequencies at different temperatures. It follows from the frequency dependence of the spectra that Cr3+ and Fe3+ ions are characterized by a continuous fine-structure parameter distribution in the range 0.06-0.55 cm-1 for Cr3+ and 0.04-0.33 cm-1 for Fe3+. The simulations of these spectra are computed with a fine-structure parameter distribution P(h20, lambda ) whose expression is determined by analogy with the distribution of electric field gradient P(Vzz, eta ) developed by Czjzek considering amorphous solids with random ionic coordination. An excellent agreement between observed and calculated spectra is obtained whatever the frequency band.

Modeling EPR Powder Spectra Using Numerical Diagonalization of the Spin Hamiltonian

“…In those cases, distributions of ZFS parameters are generally no longer Gaussian, but are asymmetric or exhibit multiple modes. Modeling EPR spectra of paramagnetic centers in such disordered materials requires multiple-spectra computation (21). Future extensions of the code are in progress and will concern nonlinear inversion methods for analyzing site distributions in poorly ordered materials.…”

“…High-order perturbation calculations (16) or straightforward numerical diagonalization of the spin Hamiltonian (see, for instance, [17][18][19][20][21] are then required to determine reliable resonance fields values. For S Ͼ 3 2 , e.g., for S-state ions, the large number of allowed transitions occurring between and inside the Kramers' doublets, makes it difficult to index the EPR lines in powder studies (22,23), and even in single-crystal studies (24).…”

“…Successful attempts at computing EPR powder spectra of S Ͼ 3 2 centers using numerical diagonalization of the spin Hamiltonian are reported in the literature (17)(18)(19)(20)(21). However, among these works, none deals with complex (S ϭ…”

Is Electron Paramagnetic Resonance a Valuable Technique for Structural Study of PZG Glass through Recrystallization?

“…Although XRD spectra suggest a similar crystalline state for recrystallized and crystalline PbGaF 5 powder, the EPR spectra differ by the resonance relative ) be responsible for the high-intensity resonance at g eff ϭ ͗0.24). The XRD spectrum of deposited GaF 3 is typical of 2.0 in the recrystallized compound, as it is in TMFG (20). amorphous compounds.…”

Structural Fe3+ in Natural Kaolinites: New Insights from Electron Paramagnetic Resonance Spectra Fitting at X and Q-Band Frequencies

“…Therefore, such EPR spectra cannot be interpreted using only one set of fine-structure parameters. Studies using parameterized distributions have been used successfully to model the EPR spectra of Cr 3+ and Fe 3+ in glasses (Legein et al, 1995). A crystal field distribution was also proposed for the interpretation of the X-band EPR spectra of kaolinites (Bonnin et al, 1982), but this approach was of limited utility because it was restricted to the distribution of the rhombicity parameter, i.e., the ratio of second-order fine-structure parameters (h = BZ/B2~ In the present study, the two-dimensional distribution of both B ~ and B 2 parameters are determined to extract information regarding the site-to-site variations of the crystal field around Fe 3+ ions.…”