A neutron diffraction study of the d0 and d10 lithium garnets Li3Nd3W2O12 and Li5La3Sb2O12

The garnets Li3Nd3W2O12 and Li5La3Sb2O12 have been prepared by heating the component oxides and hydroxides in air at temperatures up to 950 degrees C. Neutron powder diffraction has been used to examine the lithium distribution in these phases. Both compounds crystallise in the space group Ia3d with lattice parameters a = 12.46869(9)angstrom (Li3Nd3W2O12,) and a = 12.8518(3),angstrom (Li5La3Sb2O12). Li3Nd3W2O12 contains lithium on a filled, tetrahedrally coordinated 24d site that is occupied in the conventional garnet structure. Li5La3Sb2O12 contains partial occupation of lithium over two crystallographic sites. The conventional tetrahedrally coordinated 24d site is 79.3(8)% occupied. The remaining lithium is found in oxide octahedra which are linked via a shared face to the tetrahedron. This lithium shows positional disorder and is split over two positions within the octahedron and occupies 43.6(4)% of the octahedra. Comparison of these compounds with related d(0) and d(10) phases shows that replacement of a d(0) cation with d(10) cation of the same charge leads to an increase in the lattice parameter due to polarisation effects. (c) 2007 Elsevier Inc. All rights reserved.