The radiation resistance of silica and silica-based mirrors to synchrotron radiation is relatively low compared with that of a number of ceramic materials, of which silicon carbide has been studied most extensively, although other materials such as the hafnium carbides and nitrides have generally better X-ray reflective properties. The polishabilities of various types of silicon carbide, having microstructures which range from very homogeneous to a coarse porosity have been investigated, as well as that of one type of titanium nitride. All the materials are capable of being polished to a very high degree, and surface finishes of a few tenths of a nanometre peak to valley have been attained.
M. J. Hanney,
"Ceramic Materials As Mirrors For Synchrotron Radiation", Proc. SPIE 0315, Reflecting Optics for Synchrotron Radiation, (3 May 1982); doi: 10.1117/12.933001; https://doi.org/10.1117/12.933001