ENDOR investigation of cubic Fe³⁺centres in NaCl single crystals

Abstract

Cubic Fe3+ centres in NaCl single crystals have been studied with electron nuclear double resonance (ENDOR) at T=17 K. The superhyperfine (SHF) and quadrupole interactions of the paramagnetic ion with the nearest set of four Cl- anions and the second-nearest set of twelve Na+. Cations have been determined. The results confirm the structural model of an Fe3+ ion at a tetrahedrally symmetric interstitial position with the nearest four Na+ cations missing, as suggested previously from the analysis of the SHF structure of their EPR spectra.

Electron - nuclear double-resonance study of a substitutional defect complex in x-irradiated NaCl crystals

“…By further annealing above 250 K or by x-irradiation at room temperature (RT), the orthorhombic Fe 3+ centres are converted into cubic Fe 3+ cub centres. As suggested previously from the analysis of the EPR superhyperfine (shf ) structure [6], and recently confirmed by electron-nuclear double-resonance (ENDOR) spectroscopy [7], the Fe 3+ cub centre consists of an interstitial Fe 3+ ion with its four nearest Na + neighbours missing. As far as we are aware, the presence of such an interstitial cation in the compact NaCl lattice which is known to exhibit a predominant Schottky type of disorder [8] had not been reported before.…”

“…Compared to the case for the cubic Fe 3+ centres studied previously [7], ENDOR measurements of the orthorhombic Fe 3+ (I) centres are complicated by the fact that, due to the large ZFS parameters, the EPR transitions extend over a large magnetic field range and are highly anisotropic. The EPR lines labelled x, y, and z in figure 1 were chosen for the ENDOR measurements because in the X band they are well separated from the other lines as well as from the EPR lines of the Fe + centre.…”

“…Stationary ENDOR experiments, as well as some EPR measurements, were performed with the same custom-built, computer-controlled X-band spectrometer as was employed in our previous studies on Fe 3+ cub centres [7]. The best stationary ENDOR spectra were obtained at T = 15 K.…”

Dynamics of self-trapped hole processes in AgCl

“…Also, Hay et al [6] showed that lowtemperature irradiation with band-gap light could also produce a trigonally symmetric centre, Fe 3+ trig , with only three cation vacancies bound to the interstitial Fe 3+ ; at higher temperatures, this converts to the cubic centre Fe 3+ cubic , described above. The cubic centre is apparently stabilized by the binding energy of the tetrachloroferrate ion; it has also since been seen in other hosts, such as Fe-doped NaCl [7][8][9].…”

Theoretical Investigation of the Spin Hamiltonian Parameters for the Tetragonal [Fe(CN)₄Cl₂]^5– Complex in NaCI

“…Sodium chlorine (NaCl) single crystal is usually regarded as a model system for investigations of the structural and magnetic properties of the doped transition-metal impurities. Especially, NaCl containing iron exhibit interesting magnetoplastic [1], crystallization [2] and electronic and local relaxation [3] properties as well as unique magnetic resonance and electron nuclear double resonance behaviours [4][5][6]. These properties or behaviours may be closely related to the local crystal field environments of the doped iron impurities in the hosts, and the above properties can be conveniently studied by means of the electron paramagnetic resonance (EPR) technique.…”