Thesis

The low-temperature formation of mixed-metal oxides

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Awarding institution
  • University of Strathclyde
Date of award
  • 2011
Thesis identifier
  • T12873
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Abstract
  • This thesis describes a new route to lithium molybdate, Li?MoO?, which involves grinding together LiOH·H?O and MoO? in air at room temperature. X-ray powder diffraction data show that the formation of highly crystalline Li?MoO? 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 Li?MoO? grown from aqueous solution [R3 ; a = 14.3178(14) A?, c = 9.5757(9) A?]. 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·H?O. In this manner, Li?MoO? 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 (HLaTiO?, H?SrTa?O? and H?La?Ti?O??), with a controlled proton and lithium content. This involves grinding a stoichiometric quantity of LiOH·H?O with each of the solid acids. X-ray powder diffraction data show that the reactions leading to H??xLixLaTiO? [P4/nmm; x ? 0.1] and HLiSrTa?O? [Ama2] are complete after 5 d, whilst those leading to H???xLi?xLa?Ti?O?? [I4/mmm; x ? 0.125] are complete after 53 min. Neutron powder diffraction data of the intermediate members of the H??xLixLaTiO? 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: ???xLixLaTiO?[(??x)/?] (0.5 ? x ? 0.9), ?LiSrTa?O?.? and ?LiLa?Ti?O?.?. AC impedance spectroscopy measurements indicate that these samples demonstrate a lower total ionic conductivity than that of the respective lithium end-members.
Resource Type
DOI
Date Created
  • 2011
Former identifier
  • 832998

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