LOW-ENERGY EXCITATIONS IN POLYVINYL-CHLORIDE - RAMAN-SCATTERING AND THERMAL-PROPERTIES

The low-energy excitations of a very fragile glass-former (in the sens e of Angell), poly(vinyl chloride), have been studied by low-frequency Raman scattering and by measurements of the low-temperature heat capa city and thermal conductivity. Two different samples were investigated : one with a crystallinity of about 15%, the other quenched and amorp hous, as measured by small-angle neutron scattering. The boson peak in Raman scattering was observed in both samples even at room temperatur e. A clear correspondance between the Raman boson peak, the excess of heat capacity and the plateau of thermal conductivity was shown. It is confirmed that the boson peak or the heat capacity excess are relativ ely small in this very fragile glass-former. However it is deduced tha t the high concentration of tunnelling systems in the amorphous sample is the result of a rapid quenching rather than an intrinsic property of fragile glass-formers.