Thomas W. S. Yip

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

The garnets Li{sub 3}Nd{sub 3}W{sub 2}O{sub 12} and Li{sub 5}La{sub 3}Sb{sub 2}O{sub 12} have been prepared by heating the component oxides and hydroxides in air at temperatures up to 950deg. C. Neutron powder diffraction has been used to examine the lithium distribution in these phases. Both compounds crystallise in the space group Ia3-bard with lattice parameters a=12.46869(9)A (Li{sub 3}Nd{sub 3}W{sub 2}O{sub 12}) and a=12.8518(3)A (Li{sub 5}La{sub 3}Sb{sub 2}O{sub 12}). Li{sub 3}Nd{sub 3}W{sub 2}O{sub 12} contains lithium on a filled, tetrahedrally coordinated 24d site that is occupied in the conventional garnet structure. Li{sub 5}La{sub 3}Sb{sub 2}O{sub 12} 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{sup 0} and d{sup 10} phases shows that replacement of a d{sup 0} cation with d{sup 10} cation of the same charge leads to an increase in the lattice parameter due to polarisation effects.

Ion exchange and structural ageing in the layered perovskite phases H1-xLixLaTiO4

Grinding together the solid acid HLaTiO4 with stoichiometric quantities of lithium hydroxide monohydrate gives the solid solution H(1-x)Li(x)LaTiO4. The structures of these crystalline phases have been refined against neutron powder diffraction data to show that all of these compounds crystallize in the centrosymmetric space group P4/nmm. The protons and lithium cations occupy sites between the perovskite layers; the former in hydroxide groups that hydrogen-bond to adjacent layers while Li(+) is in four-coordinate sites that bridge the perovskite slabs with a geometry intermediate between square-planar and tetrahedral. The reaction proceeds rapidly, but the unit cell size continues to evolve over the course of days with a gradual compression along the interlayer direction that can be modeled using a power law dependence reminiscent of an Ostwald ripening process. On heating, these materials undergo a mass loss because of dehydration but retain the layered Ruddlesden-Popper structure up to 480 °C before a substantial loss of crystallinity on further heating to 600 °C. Impedance spectroscopy studies of the dehydrated materials shows that Li(+) mobility in these materials is lower than the LiLaTiO4 end member, possibly because of microstructural effects causing large intergrain resistance through the defective phases.

An eco-friendly, tunable and scalable method for producing porous functional nanomaterials designed using molecular interactions

Abstract Despite significant improvements in the synthesis of templated silica materials, post‐synthesis purification remains highly expensive and renders the materials industrially unviable. In this study this issue is addressed for porous bioinspired silica by developing a rapid room‐temperature solution method for complete extraction of organic additives. Using elemental analysis and N2 and CO2 adsorption, the ability to both purify and controllably tailor the composition, porosity and surface chemistry of bioinspired silica in a single step is demonstrated. For the first time the extraction is modelled using molecular dynamics, revealing that the removal mechanism is dominated by surface‐charge interactions. This is extended to other additive chemistry, leading to a wider applicability of the method to other materials. Finally the environmental benefits of the new method are estimated and compared with previous purification techniques, demonstrating significant improvements in sustainability.