[1] Fdn Res & Technol Hellas FORTH ICE HT, Inst Chem Engn & High Temp Chem Proc, Patras 26504, Greece
[2] Acad Sci Czech Republ, J Heyrovsky Inst Phys Chem, Vvi, CR-18223 Prague 8, Czech Republic
[3] Tech Univ Berlin, Inst Festkorperphys, D-10623 Berlin, Germany
[4] Univ Manchester, Sch Phys & Astron, Manchester M13 9PL, Lancs, England
[5] Univ Patras, Dept Mat Sci, Patras 26504, Greece