Mechanistic Insights into the Structure-Property Relationship through detailed Crystallographic Studies

Main list: Special Seminars

Abstract

Mark Senn
University of Oxford

Engineering a ground state structure to produce a desired physical property is becoming more widespread, particularly in the field of ferroelectrics where the symmetry of the paraelectric parent phase may be intentionally broken by chemical design to lead to a polar distortion, e.g., Ref. 1.  Here it is our ability to characterise the structure via crystallographic methods and qualify its average symmetry which allows us to inform the structure-property relationship which underpins this work.  I will give two examples from my own research where symmetry analysis of the ground state crystallographic structure has led to mechanistic insight into metal-insulator phase transitions2 and improper ferroelectric mechanisms3.

However, despite the success of this approach, several limitations exist.  Firstly, many physical properties such as thermal expansion and superconductivity do not arise solely from the ground state crystal structure but due to excitations and lattice dynamics.  Secondly, not all functional materials are fully ordered and their physical properties often arise from so called order-disorder phase transitions.  Here, long-range crystallographic symmetry does not reflect the local underlying microscopic mechanism, and it is unclear what insight conventional crystallography can bring.  In the second half of my talk I will extend the application of symmetry analysis further to tackle these problems.  I will show how we can gain insight into negative thermal expansion though the study of closely competing ground state structures3 and how in the archetypal ferroelectric Barium Titanate we can reconcile the observed order-disorder phase transitions with its long range crystallographic symmetry and its observed macroscopic properties4.

 

References:

1)      A. T. Mulder, N. A. Benedek, J. M. Rondinelli, C. J.  Fennie, Adv. Funct. Mater. 23, 4810–4820 (2013).

2)      M.S. Senn, J.P. Wright, and J.P. Attfield, Nature 481, 173 (2012).

3)      M.S. Senn, A. Bombardi, C.A. Murray, C. Vecchini, A. Scherillo, X. Luo, and S.W. Cheong, Phys. Rev. Lett. 114, 23 (2015).

4)      M.S. Senn, D.A. Keen, T.C.A. Lucas, J.A. Hriljac, and A.L. Goodwin, http://arxiv.org/abs/1512.03643 (2015).

  • Venue

    113 - Seminar Room, BMS Building, University of St. Andrews, St. Andrews, Fife, Scotland

  • Date

    January 22, 2016

  • Time

    From: 14h00 To: 15h30

  • Sponsor

    University of St Andrews
    The oldest university in Scotland, with international renown for both research and education of undergraduates and postgraduates.

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