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A mössbauer spectroscopy study of an anhydrous non-stoichiometric europium (III) chloride phase

1983; Elsevier BV; Volume: 95; Issue: 1 Linguagem: Inglês

10.1016/0022-5088(83)90397-1

1878-2728

Jonathan Ball, Charles M. Jenden, Samuel J. Lyle, William A. Westall,

Luminescence Properties of Advanced Materials

Anhydrous europium (III) chloride, when heated under vacuum at temperatures above 570 K, decomposes according to the overall reaction EuCl3(s) → EuCl2(s) + 125Cl2(g) A non-stoichiometric chlorine-deficient phase with the hexagonal UCl3-type structure is observed down to at least a europium-to-chlorine ratio of 1:2.84. Samples of composition EuCl> 2.8 were examined by Mössbauer spectroscopy, X-ray diffraction and electrical conductivity techniques. The temperature-dependent Mössbauer spectra provide, for the first time, evidence for electron exchange between neighbouring europium sites in a non-stoichiometric europium compound. The activation energy Ea for electron mobility above about 200 K is 0.083 ± 0.003 eV for EuCl2.96 from electrical conductivity measurements. This value for Ea is in agreement with others derived from the Mössbauer spectra using an electron hopping model according to which a potentially mobile electron is bound at each site for an average time which is a function of temperature. Chemical isomer shifts and ratios of recoil-free fractions (Lamb-Mössbauer factors) for europium (II) to europium (III) are also derived from the spectra. Lattice parameters obtained from X-ray data are discussed in relation to those for the stoichiometric EuCl3.00 phase.