Simon Redfern

Nanyang Technological University, Asian School of The Environment, Faculty Member

University of Cambridge, Department of Earth Sciences, Faculty Member

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Dean of the College of Science and President's Chair in Earth Sciences (Asian School of the Environment & School of Materials Science and Engineering), NTU Singapore.
Emeritus Professor in Mineral Physics, Department of Earth Sciences, University of Cambridge (and former Head of Department)
Emeritus Fellow, Jesus College, University of Cambridge
Supervisors: Ekhard Salje

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Siddharth S Saxena

University of Cambridge

Jayjit Majumdar

University of Kalyani

Waltraud M. Kriven

University of Illinois at Urbana-Champaign

Nicolas Coltice

École Normale Supérieure

Bob Myhill

University of Bristol

David Seamon

Kansas State University

Yavor Shopov

Sofia University "St. Kliment Ohridski"

Alexander Korsunsky

University of Oxford

Armando Marques-Guedes

UNL - New University of Lisbon

Gabriel Gutierrez-Alonso

University of Salamanca

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Books by Simon Redfern

Transformation Processes in Minerals

Phase transformations occur in most types of materials, including ceramics, metals, polymers, div... more Phase transformations occur in most types of materials, including ceramics, metals, polymers, diverse organic and inorganic compounds, minerals, and even crystalline viruses. They have been studied in almost all branches of science, but particularly in physics, chemistry, engineering, materials science and earth sciences. In some cases the objective has been to produce materials in which phase transformations are suppressed, to preserve the structural integrity of some engineering product, for example, while in other cases the objective is to maximise the effects of a transformation, so as to enhance properties such as superconductivity, for example. A long tradition of studying transformation processes in minerals has evolved from the need to understand the physical and thermodynamic properties of minerals in the bulk earth and in the natural environment at its surface. The processes of interest have included magnetism, ferroelasticity, ferroelectricity, atomic ordering, radiation damage, polymorphism, amorphisation and many others-in fact there are very few minerals which show no influence of transformation processes in the critical range of pressures and temperatures relevant to the earth. As in all other areas of science, an intense effort has been made to tum qualitative understanding into quantitative description and prediction via the simultaneous development of theory, experiments and simulations. In the last few years rather fast progress has been made in this context, largely through an interdisciplinary effort, and it seemed to us to be timely to produce a review volume for the benefit of the wider scientific community which summarises the current state of the art. The selection of transformation processes covered here is by no means comprehensive, but represents a coherent view of some of the most important processes which occur specifically in minerals.

Papers by Simon Redfern

The temperature dependence of the cation distribution in synthetic hercynite (FeAl2O4) from in-situ neutron structure refinements

American Mineralogist, Oct 1, 1998

The temperature dependence of the cation distribution in synthetic hercynite (FeAl 2 O 4 ) has be... more The temperature dependence of the cation distribution in synthetic hercynite (FeAl 2 O 4 ) has been determined using in-situ time-of-flight neutron powder diffraction. The sample was synthesized from the oxides under controlled oxygen fugacity and then quenched in air. Neutron diffraction patterns were then collected under vacuum on heating from room temperature to 1150 ЊC, and the cation distribution was determined directly from site occupancies obtained by Rietveld refinement. The degree of inversion, x, decreased from 0.135(4) at room temperature to 0.112(4) at 600 ЊC. Thereafter the degree of inversion increases smoothly with increasing temperature, reaching a value of 0.219(5) at 1150 ЊC. The decrease in x on heating to 600 ЊC is a kinetic phenomenon caused by the system moving toward its equilibrium degree of order from the relatively disordered state maintained after quenching from the synthesis temperature. The equilibrium ordering behavior between 600 and 1150 ЊC has been analyzed using both the O'Neill-Navrotsky and Landau thermodynamic models. Although the data could be fitted with both models over the temperature range of the measurements, Landau theory predicts the incorrect curvature of the equilibrium x-T curve, leading to a significant discrepancy in the calculated behavior when the model is extrapolated outside the calibrated temperature range. The correct x-T curvature is predicted by the O'Neill-Navrotsky model, and values of the model coefficients ␣ ϭ 31.3 Ϯ 1.1 kJ/mol and ␤ ϭ 19.7 Ϯ 3.4 kJ/mol were obtained by least-squares fitting to the equilibrium data. This confirms the results of a previous study using quenched material, which suggested that the sign of the ␤ coefficient in FeAl 2 O 4 is opposite to that found in other 2-3 oxide spinels.

Simon Redfern

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