Creep was measured for glasses in the system of As-Se by a torsional method under a constant torque in the glass transition range. Compliance,
J(t), of retarded elasticity can be normally described as
J(t)=∑
iJi(1-
e-t/τi) (1)
where
t is time and τ is retardation time. When
i was even 1, a correlation coefficient obtained for each run was higher than 0.95 and thus it was considered that calculated curves (at
i=1) fitted well with the measured ones.
The micro-viscosity, η
G, of retarded elasticity (Fig. 1) can be obtained by using τ and
J∞ (compliance at the final stage in each run, ≅1/
G2). The plots of log η
G agaist 1/
T gave essentially a straight line for each sample as shown in Fig. 6. Thus the apparent activation energy for the process of deformation due to retarded elasticity was calculated by the following equation,
ΔEηG=
R⋅d(logη
G)/d(1/
T), where
R is the gas constant. The activation energy was approximately one-half of that for viscous flow as shown in Fig. 7 and was lower than the bonding energy of As-Se.
Final compliance,
J∞, showed a maximum at η≅10
14 poise in every composition of As-Se glasses. The following equation expressed as a function of viscosity is proposed,
J∞=(1-
k2η
G/η)(
f1[
k1/η]+
f2[
nk1/η]) (10)
where
k1,
k2,
n,
f1 and
f2 are parameters for fitting. When [
k1/η] and [
nk1/η] exceed 1, they were always replaced by 1. This equation means that
J∞ is mainly dominated by the term, (1-
k2η
G/η), in lower viscosity range (η<10
14 poise), while in higher viscosity range (η>10
14 poise) it is controlled by the term, [
k1/η] or [
nk1/η]. The term (1-
k2η
G/η) formulates the competition between η
G and η, and the terms [
k1/η] and [
nk1/η] can be attributed to the interactions of layers in glass structure. The calculated curves based on Eq. (10) agreed well with the measured values as shown in Fig. 8 (a), (b) and (c).
Coefficient
f1 was found to decrease with increasing Se content and
f2 increased conversely with Se content (Fig. 10). Though
k2 should theoretically be equal to 1, it decreased with As content. In addition, it was found that
f2 and
k2, when they were plotted against the Se atom fraction, changed appreciably their slopes at Se≅80 atom% (around As
2Se
8) as shown in Figs. 9 and 10. It was therefore presumed that
f1 would depend on the ring structure of network and
f2 and
k2 would depend on the chain structure.
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