Browsing by Author "Greaves, TL"

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    Crystal structure of protic ionic liquids and their hydrates
    (International Union of Crystallography, 2021-08-14) Hassett, MP; Brand, HEA; Binns, J; Martin, AV; Greaves, TL
    Protic Ionic Liquids (PILs) are a class of tailorable solvents made up of fused salts with melting points below 100 °C, which are formed through a Brønsted acid-base reaction involving proton exchange[1]. These solvents have applications as lubricants, electrolytes, and many other uses[2]. Although they are quite similar to molten salts, their crystal structures have not been explored in-depth, with only ethylammonium nitrate (EAN) having a reported crystal structure[3, 4]. Ten alkylammonium-based protic ionic liquids at both neat (<1 wt% water) and 90 mol% PIL, 10 mol% water concentrations were selected. Diffraction patterns were collected at the Australian Synchrotron ANSTO while attempting to crystallise the samples by cooling to 120 K. Five samples crystallised (3 neat, 2 dilute), where the temperature of the system was then increased at a rate of 6 K/min to room temperature. From these patterns we have identified a number of crystal phases, identifying their stability ranges and lattice constant variation from 120 K to room temperature. © 2021 The Authors
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    Structure and dynamics in photovoltaic metal hydrides
    (Australian Institute of Physics, 2018-01-30) Chea, K; Greaves, TL; Le, T; Rule, KC; Mole, RA; Wang, P; Shrestha, S; Conibeer, G; Iles, GN
    Solar cell technology is an active area of research with the quest to improve the efficiency of solar cells to above the current value of 44%. Hot carrier solar cells are particular types of cells which may enable higher efficiencies to be obtained. However, these are only feasible where there is a sufficiently large band gap in the phonon dispersion of the bulk material to minimise energy loss to thermalisation, thus keeping the electrons ‘hot’. Binary compounds with a large mass difference between the two constituent atoms, and high level of crystal symmetry such as titanium hydride, can have such a gap in their phonon dispersion. Titanium hydride is an interesting photovoltaic material with a broad range of properties, which vary depending on the proportion of hydride present. Theoretical studies show TiH2 has a phonon band gap of 95 meV in the bulk phase, however, experimentally this compound exists as a powder because the hydrogenation process causes large stresses in the lattice which are strong enough to crack the bulk sample. For solar cell absorber materials, a bulk sample is preferred and these can be manufactured by hydrogenating very pure Ti metal. We have previously studied TiH1.65 using X-ray powder diffraction and inelastic neutron scattering and found that while the width of the acoustic and optical phonon bands is different from those of TiH2, it did have a phonon band gap of 65 meV i.e. large enough to block Klemens’ decay. We present here an extension of this work with Fourier Transform Infra-red (FTIR) and Raman spectroscopy, along with X-Ray Diffraction (XRD) data from the photovoltaic materials, TiH2 and ZrH2.
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    Understanding order and correlation in liquid crystals by fluctuation scattering
    (Australian Nuclear Science and Technology Organisation, 2021-11-26) Binns, J; Adams, P; Kewish, CM; Greaves, TL; Martin, AV
    Characterising the supramolecular organisation of macromolecules in the presence of varying degrees of disorder remains one of the challenges of macromolecular research. Discotic liquid crystals (DLCs) are an ideal model system for understanding the role of disorder on multiple length scales. Consisting of rigid aromatic cores with flexible alkyl fringes, they can be considered as one-dimensional fluids along the stacking direction and they have attracted attention as molecular wires in organic electronic components and photovoltaic devices. With its roots in single-particle imaging, fluctuation x-ray scattering (FXS) is a method that breaks free of the requirement for periodic order. However, the interpretation of FXS data has been limited by difficulties in analysing intensity correlations in reciprocal space. Recent work has shown that these correlations can be translated into a three-and four-body distribution in real space called the pair-angle distribution function (PADF) – an extension of the familiar pair distribution function into a three-dimensional volume. The analytical power of this technique has already been demonstrated in studies of disordered porous carbons and self-assembled lipid phases. Here we report on the investigation of order-disorder transitions in liquid crystal materials utilising the PADF technique and the development of facilities for FXS measurements at the Australian Synchrotron. © 2021 The Authors