Structural chemistry and spin-glass behaviour of Nd18Li8Fe4TiO39

Nd18Li8Fe4TiO39 has been synthesised and characterised by neutron powder diffraction, X-ray absorption spectroscopy, Mössbauer spectroscopy and magnetometry. The cubic structure (Pm3̄n, a=11.97227(8) Å) is based on intersecting 〈1 1 1〉 chains comprised of alternating octahedral and trigonal-prismatic coordination sites. These chains lie within hexagonal-prismatic cavities formed by a Nd–O framework. The larger of the two crystallographically distinct octahedral sites, 8e, is occupied by iron, titanium and lithium in a ratio of 76:20:4; the smaller, 2a, is occupied by iron and titanium in a ratio of 79:21. The trigonal-prismatic site, 16i, is occupied by lithium and iron in a ratio of 98:2. The cations on the 2a sites are assigned as Ti4+and low-spin Fe4+, and those on the 16i sites as Li+ and Fe3+. The 8e sites are thought to be occupied by Li+, Fe3+ and Ti3+. Nd18Li8Fe4TiO39 undergoes a transition to a spin-glass state at 4.25(5) K.