Specialty Optical Fibers Handbook

with unstabilized zirconia experience large strains when the zirconia changes

structure leading to coating microcracks [30]. It is recommended that zirconia be

stabilized with yttria (Y

2

O

3

) to force a stable cubic structure [29]. The monoclinic

form of zirconia has a CTE of 6:5  10

6

=



C at 1000 8C and the stabilized cubic

form 10:5  10

6

=



C at 1000 8C [31]. When zirconia is stabilized, the strain is

reduced, but residual strain results from the difference in CTEs between the

sapphire and stabilized zirconia; this will likely result in strength degradation

[30]. Zirconia will react with hydrochloric and nitric acids, but it is stable in

oxidizing and moderately reducing atmospheres. At 2000 8C, zirconia will react

with refractory carbides and stabilized ...