Evangelia A. Pavlatou

E.A. Pavlatou

Proceedings of the International George Papatheodorou Symposium (1999), Patras, Greece, September 17-18, p.151-156 (poster)

Raman spectra of the binary BiCl₃-KCl system have been measured at various compositions in the liquid and glassy states. The temperature and composition dependence of the reduced Raman spectra have shown that for low concentrated mixtures in BiCl₃ (XBiCl₃≤0.25) the liquid structure is possibly characterized by the presence of octahedral species BiCl₆^3-. The spectral characteristics of the mixtures rich in BiCl₃ indicate that except for the octahedral species BiCl₆^3- lower symmetry species like BiCl₄^- seem to be formed in the melt. The overall spectral behaviour may be associated with the existence of distorted octahedral BiCl₆^3- and tetrahedral BiCl₄^- probably bounded by corners and/or edges forming short length polymeric units and consequently in the case of pure BiCl₃ a "loose" network type structure could be assumed. Molecular dynamic simulations of the pure molten have been performed using a polarisable ionic potential. The computer simulations shows that the structural motif is viewed as Bi³⁺ ions having coordination number four, five and six. The calculated frequencies of the symmetric breathing vibrational modes of the octahedra/tetrahedra present in the melt accord rather closely to those observed experimentally.    

E.A. Pavlatou, G.N. Papatheodorou

Proceedings of the International Symposium in Honour of Terje Ostvold Conference (1998), Roros, Norway, November 1-3, p. 205-214 (oral)

Raman spectra of solid and liquid beryllium chloride and of binary liquid BeCl₂-CsCl mixtures have been measured. Systematic investigation of the Raman spectra upon heating crystalline forms of BeCl₂, revealed two different solid phase transitions at about 250 and 400°C, apart from the crystallization of the glass at -220°C. The vibrational spectra of crystalline modifications α and β were further analyzed using available crystallographic data. The Raman spectra of solid and liquid BeCl₂ indicate that the structure in the melt consists of finite chains of edge-sharing tetrahedra, which are terminated at both ends by BeCl₃ units. The two-dimensional polymeric-like structure of the pure melt breaks up continuously with addition of CsCl forming charged polymeric chains. In mixtures rich in CsCl, the spectral changes with temperature and composition variation reflect an equilibrium involving two ionic species BeCl₄^2- and BeCl₃^-.