TYC Lunchtime Seminar: Towards a mechanistic understanding of proton transfer ferroelectricity

Abstract:

While most ferroelectric research is focused on inorganic ceramics, molecular ferroelectrics have been shown to offer large spontaneous polarization and high Curie temperatures. However, the mechanism of their ferroelectric switching is poorly understood. We explore proton tautomerism in the prototypical case of croconic acid [1].

The mechanism of ferroelectric phase transitions is conventionally investigated by constructing an effective Hamiltonian whose degrees of freedom are derived from the unstable gamma point phonon modes of the crystal. While this has been successful in the case of barium titanate [2], we have determined that this approach would not succeed for croconic acid by analysing the minimum energy path between the structural ground states as produced by the nudged elastic band algorithm [3]. We subsequently consider alternative schemes for an effective Hamiltonian for croconic acid.

[1] S. Horiuchi, Y. Tokunaga, G. Giovannetti, S. Picozzi, H. Itoh, R. Shimano, R. Kumai and Y. Tokura, Nature, 2010, 463, 789–792.

[2] W. Zhong, D. Vanderbilt and K. M. Rabe, Phys. Rev. B, 1995, 52, 6301–6312.

[3] H. Jonnson, in Classical and Quantum Dynamics in Condensed Phase Simulations, ed. B. J. Berne, G. Ciccotti and D. F. Coker, World Scientific, 1998, ch. 16, pp 385-404.