Fe3+ ions in amorphous solids: EPR on mechanically and chemically amorphized Al2O3

Abstract

Stepwise amorphization of a low-level doped a-Al 2 03 single crystal yielded powders without changes of the concentration and chemical nature of the dopants. Kind and degree of disturbances could be unambiguously monitored by the allowed and forbidden transitions of the Fe 3 '-cw-EPR in X-band using a Bruker bimodal cavity. Based on simulations diagonalizing the spin Hamiltonian for S = 5/2 it was possible to discriminate between regions as well as samples of structural order and disorder. The spectral pattern of the allowed and forbidden transitions of Fe" ions together with the field-position-dependent saturation behaviour (4.2 K) allowed us to differentiate between crystalline and amorphous components or regions of a sample.

Electron paramagnetic resonance investigations of -Al2O3powders doped with Fe3 ions: experiments and simulations

“…The X-band spectra obtained with parallel mode detection (B 1 B 0 ) for the different samples are shown in figure 9. The spectrum of sample I was first published by Scholz and Stösser [31]. The experimental spectra are well reproduced, applying the parameter sets deduced from the normal mode detection spectra (cf figure 9 and tables 1 and 2).…”

Local structural orders in nanostructured Al2O3prepared by high-energy ball milling

“…Figure 9 shows experimental X-band (9.3 GHz) EPR spectra of the unmilled α-Al 2 O 3 and milled samples for different milling times measured at room temperature and 4.2 K. At least, four distinct paramagnetic species are evidenced: (i) The x-band signals at effective g-values g ∼ 13, g ∼ 5.2, g ∼ 2.0 are characteristic of isolated Fe 3+ ions in crystalline corundum powder [17]. Their intensities 6 decrease very fast with increasing milling time.…”

Aluminum Fluoride as a Storage Matrix for Atomic Hydrogen

“…The signals with isotropic chemical shifts of d À 45.2 ( 29 Si MAS-NMR) and 30.4 ( 11 B MAS NMR) indicate a local environment consisting of BN 3 and SiN 4 units, as confirmed by a comparison to the spectra of the binary model compounds h-BN and a-Si 3 N 4 and b-Si 3 N 4 , respectively. [5] The intermediate-range order, originating in the interconnection of the polyhedra to give the resulting amorphous network, was traced by employing rotational echo double resonance (REDOR) NMR spectroscopy. [6] In this approach, the heteronuclear dipolar interaction between two nuclear species I and S, averaged out under the conditions of the MAS experiment, is reintroduced by rotor-synchronized 1808 dephasing pulses for the S spins.…”