Dr Ivana Evans
(email at email@example.com)
My research interests are in the area of solid state chemistry and structure-property relationships of functional materials across the chemical spectrum. Properties of materials and hence their practical applications are intimately linked to their three-dimensional structures. By understanding the structures, we aim to understand the behaviour of materials and feed this knowledge back into our synthetic efforts, with the ultimate aim of making new functional materials with improved properties and prospects for practical applications.
Current research projects are focussed on three main areas: development of new oxide ion conductors1-5, hydrogen-bonded organic functional materials6-7 and polymorphism8-9. These projects encompass synthetic work (solid state, solvothermal, crystal growth), characterisation of static and dynamic structure (powder and single crystal X-ray and neutron diffraction, electron microscopy, total scattering, solid state NMR, inelastic/quasi-elastic neutron scattering, impedance spectroscopy) and computational modelling (ab-initio molecular dynamics, AIMD).
New oxide ion conductors
Oxide ion conductors are technologically important materials, essential for applications such as oxygen sensors and pumps, ceramic membranes for oxygen separation and partial oxidation of light hydrocarbons and solid oxide fuel cells (SOFCs), where they act as electrolytes transporting O2- ions to react with a fuel such as hydrogen in the direct clean conversion of chemical to electrical energy. Our current research focusses on the discovery of new materials with high ionic conductivity, particularly at at lower temperatures (500-750oC)1-5. Ionic mobility in solids is of fundamental significance; however, if suitable materials are found, the SOFC operating temperatures could be lowered, thus alleviating the two main problems (reliability and cost) which currently limit their widerspread use in energy generation.
We recently reported the remarkably high low-temperature ionic conductivity in Bi1-xVxO1.5+x (x = 0.087, 0.095; s~3.9 ×10-2 S/cm at 500oC) and the roles of the different structural building blocks in this process.1 We have attributed this remarkable behaviour to the simultaneous presence of three key factors: a highly polarisable sublattice with vacancies, central atoms able to support variable coordination numbers and geometries, and the rotational flexibility of the these coordination polyhedra. Importantly, the structure is a stable, pseudo-cubic 3 × 3 × 3 fluorite-based superstructure.
Figure 1: Oxide ion migration pathways in Bi1-xVxO1.5+x obtained by AIMD simulations; white displacement clouds represent space visited by oxide ions; V coordination polyhedra VOx shown in red; OBi4 groups and Bi atoms shown in yellow. (a) direct O2- exchange between VOx groups; (b) O2- exchange between VOx groups via a OBi4 tetrahedron; (c) O2- vacancy-hopping through the Bi-O subllatice.
Functional hydrogenous materials and short strong hydrogen bonds
Behaviour of protons in short strong hydrogen bonds (SSHB), including migration and ordering, has implications for charge and energy transfer in chemical and biological systems in the solid state, including ferroelectric and non-linear optical materials, magnetic coordination polymers and enzyme reactions. The aim of this project is to investigate solid-state structure and dynamics of SSHB systems with proton migration and gain insight into the specific structural features and phonon modes that drive this behaviour. Synthesis, crystallisation and variable temperature X-ray diffraction work are carried out at Durham; neutron diffraction, inelastic neutron scattering and computational modelling at the ILL in Grenoble, France.
Temperature-induced proton migration has traditionally been associated with the hydrogen bond length. Our recent experimental and computational work on the four isotopologues of 3,5-pyridinedicarboxylic acid demonstrate that a local picture of the H/D environment is insufficient to understand the migration and transfer phenomena, even in simple molecular systems. Deuterated 3,5-pyridinedicarboxylic acid exhibits deuteron migration of a magnitude unprecedented in this class of materials. Importantly, deuteron migration is significantly more pronounced (0.32 Å vs. 0.09 Å) than the proton migration. Our results provide significant new insight into how an isosymmetric phase transition and vibrational free-energy stabilisation drive this behaviour and computationally predict the isotope effect observed experimentally.6
Figure 2: Isotopologues of the 3,5-pyridinedicarboxylic acid. (a) temperature dependence of the D5-O4 and D5-N1 distances in d-35PDCA and H5-O4 and H5-N1 in h-35PDCA obtained from single-crystal neutron diffraction; (b) variable-temperature powder neutron diffraction reveals a first-order phase transition associated with remarkably large deuteron migration in d-35PDCA.
Polymorphism of pharmaceutical solids
Increasingly stringent and demanding regulatory expectations imposed on the pharmaceutical industry necessitate a full, accurate and precise characterisation of its products. This is particularly important for different polymorphs of drug molecules, since they can differ in properties which determine therapeutic performance, such as dissolution rates and bioavailability.
This project involves identification and determination of crystal structures of polymorphic pharmaceutically relevant materials, studies of thermal stability and thermodynamic relationships between polymorphs, as well as processing-induced effects (e.g. by grinding, pressing, freeze drying).8-9
Figure 3: Concomitant polymorphism in chincomeronic acid (3,4-pyridinedicarboxylic acid), commonly used as a multifunctional ligand in coordination chemistry: molecular structures of Form I (needles) and Form II (blocks) differ only in the position of one hydrogen atom, leading to different crystal structure and hydrogen bonding motifs in the solid state.
Applications of powder diffraction in archaeology and art conservation
Applications of modern analytical techniques to archaeological and art objects fall into two major areas. Archaeometric studies focus on various provenance-related issues. Conservation science deals with questions related to degradation of objects with time or under certain environmental conditions. Powder X-Ray diffraction is a valuable tool in both of these areas. It can give information about the mineralogical composition, pigments used for decoration and degradation products, thus shedding light on geographical origin, manufacture processes and period, as well as preventative or remedial conservation measures.
In these projects, we collaborate with archaeologists and conservation scientists in the UK and abroad. Recent work includes Byzantine ceramics provenancing10, (Fig. 4, in collaboration with Dr. Ljiljana Damjanovic, Faculty of Physical Chemistry, University of Belgrade, Serbia) and identification of corrosion products from an ancient Egyptian figurine (Fig. 5, in collaboration with Hannah Urquhart and Dr. Chris Caple, Department of Archaeology, Durham University).
Kuang, X. J.; Payne, J. L.; Johnson, M. R.; Evans, I. R. Angewandte Chemie International Edition 2012, 51, 690.
Kuang, X. J.; Payne, J. L.; Farrell, J. D.; Johnson, M. R.; Evans, I. R. Chemistry of Materials 2012, DOI: 10.1021/cm3008107
Kuang, X. J.; Li, Y. D.; Ling, C. D.; Withers, R. L.; Evans, I. R. Chemistry of Materials 2010, 22, 4484.
Li, Y. D.; Hutchinson, T. P.; Kuang, X. J.; Slater, P. R.; Johnson, M. R.; Evans, I. R. Chemistry of Materials 2009, 21, 4661.
Evans, I. R.; Howard, J. A. K.; Evans, J. S. O. Chemistry of Materials 2005, 17, 4074.
Ford, S. J.; Delamore, O. J.; Evans, J. S. O.; McIntyre, G. J.; Johnson, M. R; Evans, I. R. Chemistry- A European Journal, 2011, 17, 52, 14942.
Evans, I. R.; Howard, J. A. K.; Evans, J. S. O. Crystal Growth & Design 2008, 8, 1635.
Evans, I. R.; Howard, J. A. K.; Evans, J. S. O.; Postlethwaite, S. R.; Johnson, M. R. Cryst. Eng. Comm. 2008, 10, 1404.
Othman, A.; Evans, J. S. O.; Evans, I. R.; Harris, R. K.; Hodgkinson, P. Journal of Pharmaceutical Sciences 2007, 96, 1380.
Damjanovic, L.; Holclajtner-Antunovic, I.; Mioc, U. B.; Bikic, V.; Milovanovic, D.; Evans, I. R. Journal of Archaeological Science 2011, 38, 818.