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STRUCTURE AND DYNAMICS OF Ge-As-S CHALCOGENIDE GLASSES MONITORED BY LOW-FREQUENCY RAMAN SCATTERING

Y. C. Boulmetis1, C. Raptis1,* , D. Arsova2

Affiliation

  1. Physics Department, National Technical University, 15780 Athens, Greece
  2. Institute of Solid State Physics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria

Abstract

The Raman scattering spectra of several “stoichiometric” (GeS2)x(As2S3)1-x glasses have been measured over temperatures ranging from 20 K, through the respective glass transition temperature Tg and up to a temperature close to melting point. For comparisons, similar temperature-dependent Raman spectra have been obtained for the “non-stoichiometric” Ge0.30As0.10S0.60 glass which is rich in Ge in relation to the above stoichiometry. All glasses studied belong to the stress-rigid network regime (mean coordination number r 2.475). Emphasis is given on the study of the low-frequency Boson peak (BP) and, in particular, its variation with composition and temperature which is related to the dynamics of the glassy network. The relative intensity of the BP to the high-frequency main molecular band is practically composition-independent in the stoichiometric glasses, but in the non stoichiometric one is much larger, thus reflecting the higher degree of disorder in the latter. The Boson peak frequency decreases with increasing Ge-content in the (GeS2)x(As2S3)1-x glasses, while that of the Ge0.30As0.10S0.60 glass is the lowest than any stoichiometric composition, implying a higher correlation length of the medium-range order for the latter glass. The temperature dependence of the BP up to the respective Tg is manifested by either a slight smooth softening with increasing temperature, or by an almost temperature independent frequency over this range of temperatures (20 K – Tg). As Tg is approached, all glasses show discontinuous (abrupt) changes in their BP characteristics (intensity and frequency), signifying the transition to a less rigid network regime. Further increase of temperature results in a sharp drop of the BP intensity for most glasses, which implies a transition to a more ordered network. The results confirm the close correlation between the BP and the medium-range order in network glasses..

Keywords

Chalcogenide glasses, Boson peak, Glassy network dynamics, Raman spectroscopy, Temperature dependence, Phase transitions.

Submitted at: May 10, 2005
Accepted at: May 26, 2005

Citation

Y. C. Boulmetis, C. Raptis, D. Arsova, STRUCTURE AND DYNAMICS OF Ge-As-S CHALCOGENIDE GLASSES MONITORED BY LOW-FREQUENCY RAMAN SCATTERING, Journal of Optoelectronics and Advanced Materials Vol. 7, Iss. 3, pp. 1209-1216 (2005)