Quasi-elastic neutron scattering study of diffusion in Cu-Se superionic conductor

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Malaysian Nuclear Agency
Copper selenide is a mixed ionic-electronic conductor and received attention from the technological and physical point of view in particular due to a high ionic conductivity. According to [1, 2] only a fraction of Cu atoms takes part in the ionic transport in Cu{sub 2-x}Se compounds: the number of mobile atoms is about 1/3 - 1/8 of the total cation concentration in stoichiometric Cu{sub 2}Se and decreases with x causing the ionic conductivity to drop. This conclusion was based on the assumption that Cu mobility does not depend on composition. Therefore the QENS study is of interest because the width and intensity of quasi-elastic peak associated with Cu diffusion are directly related to Cu coefficient of self-diffusion and the number of mobile ions, respectively. This paper presents results of QENS measurements performed on Cu{sub 1.77}Se, Cu{sub 1.90}Se and Cu{sub 1.98}Se compounds at 313 and 430 K. We found that in Cu{sub 1.98}Se the quasielastic component is not observed in ordered non-superionic {alpha}-phase at T = 313 K, however it is clearly seen in superionic {beta}-phase at T=430 K. By contrast the Cu{sub 1.77}Se compound which is superionic at ambient temperature has relatively small quasielastic component showing little difference between 313 and 430 K. The analysis shows that fraction of Cu atoms which takes part in the ionic transport indeed decreases with x in general agreement with papers [1, 2], but not vanishes at x = 0.23. [1] R.A. Yakshibaev et al., Sov. Phys. Solid State, 26 2189 (1984) [2] M.A. Korzhuev, Phys. Solid State 40 217 (1998)
Ionic conductivity, Selenides, Copper, Stoichiometry, Diffusion, Mobility
Danilkin, S. A., Avdeev, M., Ling, C., Macquart, R., Russina, M., & Izaola, Z. (2009). Quasi-elastic neutron scattering study of diffusion in Cu-Se superionic conductor. Presented at ICNX 2009: International Conference on Neutron and X-ray Scattering 2009, Kuala Lumpur, Malaysia, 29 Jun - 1 Jul 2009.