The low-temperature formation of mixed-metal oxides

This thesis describes a new route to lithium molybdate, Li₂MoO₄, which involves grinding together LiOH·H₂O and MoO₃ in air at room temperature. X-ray powder diffraction data show that the formation of highly crystalline Li₂MoO₄ is largely complete after 10 min, and that this product crystallises with the phenacite structuretype. This structure is the same as that derived from an X-ray diffraction study of a single crystal of Li₂MoO₄ grown from aqueous solution [R3 ; a = 14.3178(14) Å, c = 9.5757(9) Å]. Differential scanning calorimetric measurements show that the reaction between the solid reagents proceeds spontaneously, even at sub-ambient temperatures, and is driven by the liberation of water from the lattice of LiOH·H₂O. In this manner, Li₂MoO₄ is prepared as mono-disperse particles, which are smaller and more regularly shaped than those yielded by other synthetic methods. This reaction has been developed further to provide a new route to the lithium ion exchange of a series of protonated Ruddlesden-Popper layered perovskites (HLaTiO₄, H₂SrTa₂O₇ and H₂La₂Ti₃O₁₀), with a controlled proton and lithium content. This involves grinding a stoichiometric quantity of LiOH·H₂O with each of the solid acids. X-ray powder diffraction data show that the reactions leading to H₁₋xLixLaTiO₄ [P4/nmm; x ≥ 0.1] and HLiSrTa₂O₇ [Ama2] are complete after 5 d, whilst those leading to H₂₋₂xLi₂xLa₂Ti₃O₁₀ [I4/mmm; x ≥ 0.125] are complete after 53 min. Neutron powder diffraction data of the intermediate members of the H₁₋xLixLaTiO₄ series indicate that the interlayer cations are disordered and remain on the 16k (H⁺) and 2b (Li⁺) sites identified in the end-member phases. The exchanged phases could be modified by dehydration at 360-480 °C to give new defective layered perovskites: ☐₁₋xLixLaTiO₄[(₁₋x)/₂] (0.5 ≤ x ≤ 0.9), ☐LiSrTa₂O₆.₅ and ☐LiLa₂Ti₃O₉.₅. AC impedance spectroscopy measurements indicate that these samples demonstrate a lower total ionic conductivity than that of the respective lithium end-members.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral-pg

Grantor dc:publisher.institution

University of Strathclyde

Year dc:date.issued

2011

Author dc:creator

• Yip, Thomas Wai Sing

DOI

10.48730/dx16-sp53

Identifier

T12873

OAI identifier oai:identifier

oai:strathclyde:rv042t11v