Grain growth anisotropy of beta-silicon nitride in rare-earth doped oxynitride glasses

Grain growth experiments in oversaturated Me-Si-Mg-O-N glasses were
carried out for six different metallic elements (Me = Sc, Lu, Yb, Y, Sm
and La). These elements all form a cation with a + 3 valence but have
increasing ionic radius. Ostwald ripening was observed for all
compositions and showed that anisotropy of growth increases with
increasing Me3+ radius. Cyclic heat treatments of the samples revealed
furthermore that growth anisotropy is controlled by the adsorption
behaviour of the cation at the interface between grain and
intergranular film. The use of elements of the same valence (Sc, Y) but
different electronic structures than the rare-earth elements (Lu, Yb,
Sm and La) showed that the electronic structure has a major role on the
adsorption behaviour of the Me3+ cation.