ESR evidence of order/disorder transitions in solids caused by dehydration

Abstract

ESR spectroscopy was used to study order/disorder phenomena in paramagnetically doped solids. The dehydration process of alurninium fluoride and oxide hydrates and aluminosilicates was examined by ESR in situ measurements as well as using thermoanalytically quenched samples. Two types of amorphous states of solids have been studied: inorganic glasses in the conventional sense and amorphous states of solids which have not passed the liquid state. The complete ESR fine structure pattern of Fe 3 § ions is susceptible with respect to order/disorder processes of the actual host matrix. Dehydration processes bear some model character in this field. A quantitative description of the disorder effects on the Fe 3 § ESR could be given on the basis of a complete spin Hamiltonian using distributions of the fourth order spin coupling parameters.

Temperature- and Gaseous Phase-Mediated Reorganization and Paramagnetic Doping of Solid Aluminum Fluorides: ESR andab InitioQuantum Chemical Studies

“…The cw-ESR measurements were carried out at 77 and 298 K with the X-band spectrometer ERS300 (Center of Scientific Instruments, Berlin-Adlershof, Germany). Simulations of the powder spectra were performed by diagonalization of the full spin-Hamiltonian matrix (8), applying an appropriate spin Hamiltonian for the S"5/2 and I"5/2 problem of Mn>.…”

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

“…All simulations presented here used a program which is based on the complete diagonalization of the full spin-Hamiltonian matrix for the S = 5/2 problem [7,8]. The calculations of the powder spectra were performed for both the allowed and the forbidden transitions (mainly occurring between the 1/2 and 3/2 manifolds).…”

“…To bring to prominence the forbidden transitions the allowed ones were artificially broadened using much larger linewidths. Statistical distributions of the zero-field splitting parameters were applied to reproduce the experimental spectra of Fe3+ incorporated into amorphous materials [7,9,10].…”

“…Figure 9c displays an ESR spectrum of such a system with a Fe content of -1 ppm. A spectral pattern results which is typical for oxygen-coordinated Fe3 + ions with Fe-O-coordination in amorphous solids (see also [7]). Although there is a very strong similarity of the spectral features, the saturation tendency at 4.2 K appears to be much smaller than that of glassy-amorphous systems.…”

“…Using kaolinite as a dehydratable layer silicate, at 580°C an amorphous product (metakaolinite, sample 9) will be formed [7,13]. Caused by traces of Fe 3 + impurities, this product yields a spectrum displayed in Fig.…”