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Struktur und Dynamik Poster: Mi., 14:00–16:30 M-P129
Determination of structural disorder in superionic AgCuSe and AgCuS
Hartmut Fuess 1 , Michael Knapp 1,2 , Daria Mikhailova 1 , Anatoliy Senyshyn 1 ,
Dmytro Trots 1,∗
1 Institute for Materials Science, University of Technology, Petersenstr. 23, 64287
Darmstadt, Germany – 2 CELLS, P.O.B 68, 08193 Barcelona, Spain
Recently the high values of ionic conductivity and ionic thermoelectromotive force
[1] renovate the practical interest for the ternary superionic (SI) compounds AgCuSe
and AgCuS. In order to explain correlations between crystal structure and high-ionic
conductivity, the time-average structure of AgCuSe and AgCuS was investigated by
synchrotron (B2, HASYLAB/DESY) and neutron elastic coherent scattering (SPODI,
FRM-II) in a wide temperature range.
The model with cations disordered between tetrahedral (8c) and octahedral (32f) sites
yields a temperature dependence for the parameters of the average structure without
any anomalies. Within this model, it is likely that cations jump in skewed
directions between nearest-neighbour tetrahedral sites via the peripheries of the octahedral
cavities. Note that diffraction results on a number of SI compounds [2] imply
that ionic conductivity can be sensitive to details of the cation redistribution between
available interstitial sites vs. temperature. Taking this into account, we can propose
a correlation between the results of the electrochemical measurements [1], which revealed
only a relatively modest increase in ionic conductivity with temperature within
SI-AgCuSe, and our diffraction results, which show no pronounced cation redistribution.
This gives strong support for the validity of the model [3]. Nevertheless, due to
the limited number of observed Bragg reflections from SI AgCuSe and AgCuS the correlations
between parameters are very strong. Therefore, a detailed analysis of diffuse
scattering is mandatory. Hence, the results on the average structure are a base for
further reverse Monte Carlo (RMC) modelling. This modelling will be done with the
RMCpow software [4], which is a development of the RMC method intended specially
for powdered crystalline materials [5]. These investigations are now in progress.
Financial support from the Bundesministerium fuer Bildung und Forschung is gratefully
acknowledged.
∗ e-mail: dmytro.trots@desy.de
[1] S. Miyatani, J. Phys. Soc. Jpn. 34 (1973) 423; M.H. Balapanov et al., Physics of
the Solid State 45 (2003) 634.
[2] S. Hull, Rep. Prog. Phys. 67 (2004) 1233.
[3] D. Trots et al., EPJ B, accepted.
[4] A. Mellergard et al., Acta Crystallogr. A55 (1999) 783.
[5] D. Keen et al., J. Phys.: Condens. Matter. 17 (2005) S15.