Page 62 - Chalcogenide Glasses for Infrared Optics

40 Cha pte r T w o

400
40%

Si 7 As 5 Te 8

Softening point 300 50% Si 5 As 5 Te 10

65%
200
Si 6 As 8 Te 26
75%
6
Si As 9 Te 45
100
0 20 40 60 80 100
Percent substitution (Ge for Si)

FIGURE 2.12 Substitution of Ge for Si in Si-As-Te glasses change in softening
point.

with the measured softening point and Knoop hardness for each
composition. Figure 2.12 shows the change in softening point of the
individual Si-As-Te glass compositions as germanium is substi-
tuted for silicon. Note the softening points all decline when germa-
nium is introduced. The chalcogenide glass plate in Fig. 2.9 shows
the first glass plate cast at TI made from a blended Si-Ge-As-Te
glass. The plate was polished and an antireflection coating was
later applied.

2.5 General Physical Properties of Chalcogenide
Glasses

2.5.1 Softening Points and Hardness
The higher the softening points, the harder the glass. Figure 2.13 shows
the plot of measured hardness for about 100 compositions plotted
against their measured softening points. Some of the glasses contained