The effect of lanthanides and nitrogen on microhardness of oxynitride glasses

The investigation of microhardness of RE-Si-Mg-O-N glasses (RE = Y, La,
Sm, Yb and Lu) containing 20-26 eq.% of nitrogen revealed a possibility
of a control of the microhardness via modification of rare-earth
element additives and by the control of nitrogen content. Lu-containing
glasses exhibit hardness, which is almost of 15% higher than that of
La-glasses. Four-percent increase in nitrogen content would result in
almost the same increase in microhardness. Microhardness of
RE-containing glass follows linear dependence on ionic radius or
cationic field strength (CFS) of the corresponding cation added in the
glass network. Yttrium, which does not belong among lanthanides, does
not fit into the linear dependence. Its deviation from linearity can be
rationalized in terms of the change of the coordination number from CN
= 6 to CN = 7 without change in valency.