Mechanical stress relaxation in inorganic glasses studied by a step-strain technique

Abstract

A computer-controlled transient viscoelastometer, which is an adaption of the Rheovibron, has been developed to study the mechanical stress relaxation of amorphous materials over a range of more than five decades in time. The instrument was used to investigate the degree of non-exponentiality of the tensile stress autocorrelation function of AgI---Ag2SO4---Ag2WO4 and Ge---As---Se glasses. Upon variation of the composition, both ternary systems show large variations of the smearing of the calorimetric glass-transition anomaly. For most cases low-noise decay functions could be observed which are well fitted by stretched exponentials. For 50AgI·25Ag2SO4·25Ag2WO4 an exceptionally broad distribution of relaxation times is found. This is consistent with the sub-Tg specific heat peak previously observed in these mixed oxyanion glasses. For pure amorphous selenium two distinct relaxation processes are observed.