Structure of dysprosium and holmium phosphate glasses by the method of isomorphicsubstitution in neutron diffraction

Abstract

The relative distribution of rare-earth ionsR3+ (Dy3+ orHo3+) in thephosphate glass RAl0.30P3.05O9.62 was measured by employing the method of isomorphic substitution in neutron diffractionand, by taking the role of Al into explicit account, a self-consistent model of the glassstructure was developed. The glass network is found to be made from corner sharingPO4 tetrahedra in which there are, on average, 2.32(9) terminal oxygen atoms,OT, at 1.50(1) Å and 1.68(9) bridging oxygen atoms,OB, at 1.60(1) Å. The networkmodifying R3+ ions bindto an average of 6.7(1) OT and are distributed such that 7.9(7) R–R nearest neighbours reside at 5.62(6) Å. TheAl3+ ionalso has a network modifying role in which it helps to strengthen the glass through the formation ofOT–Al–OT linkages. The connectivity of the R-centred coordination polyhedra in(M2O3)x(P2O5)1−x glasses, whereM3+ denotes a networkmodifying cation (R3+ or Al3+), is quantified interms of a parameter fs. Methods for reducing the clustering of rare-earth ions inthese materials are then discussed, based on a reduction offs via thereplacement of R3+ by Al3+ at fixed total modifier content or via a change ofx to increase thenumber of OT availableper network modifying M3+ cation.