Fast relaxation, boson peak, and anharmonicity in Li2O-B2O3 glasses

Glasses with a composition xLi(2)O .(1-x)B2O3 were investigated by low-frequency Raman scattering in the composition range x=0-0.28. The evolution of the quasielastic line, the boson peak, the Debye frequency, and some other glass parameters with the composition was analyzed. The frequency of the boson peak omega(b) shifts with changing x by a factor of 3 and the width of the quasielastic spectrum at room temperature is always equal to similar to 0.24 omega(b). The Gruneisen parameter of the glasses is estimated on the basis of the light scattering data for the boson peak frequency within the frames of the anharmonic model of the fast relaxation and using the sound velocity data-for the Debye frequency. The anharmonic properties are compared with the fragility of these glassformers; it is shown that the fragility increases with anharmonicity. It is shown also that the width of the glass transition region correlates with the anharmonic properties. (C) 2000 American Institute of Physics. [S0021-9606(00)70939-1].