Grain growth anisotropy of β-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.