Stefano Leoni Thursday, February 19, 2009 4:00 PM

Earth & Space Sciences Bldg., 123 (Hanson Seminar Room)

Understanding Structural Phase Transformations in Solids by Simulations: An
Overview

Stefano Leoni

Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, D-01187, Dresden, Germany.

Finding new pathways to novel materials is an open challenge in modern solid-state chemistry. Among the reasons that still prevent a rational planning of synthetic routes is the lack of an atomistic understanding at the moment of phase formation. Metastable phases are, in this respect, powerful points of access to new materials. For the synthetic efforts to fully take advantage of such peculiar intermediates, a precise atomistic understanding of critical processes in the solid state in its many
facets, that is, nucleation patterns, formation and propagation of interfaces, intermediate structures, and phase growth, is mandatory. Recently 1-10 we have started a systematic theoretical study of phase transitions, especially of processes with firstorder thermodynamics, to reach a firm understanding of the atomistic mechanisms governing polymorphism in the solid state. A clear picture is emerging of the interplay between nucleation patterns, the evolution of domain interfaces and final material
morphology. Therein intermediate metastable structural motifs with distinct atomic patterns are identified, which become exciting targets for chemical synthesis. Accordingly, a new way of implementing simulation strategies as a powerful support to the chemical intuition is emerging8,9. Simulations of real materials under conditions corresponding to the experiments are shedding
light onto yet elusive aspects of solid-solid transformations. Particularly, sharp insights into local nucleation and growth events allow the formulation of new concepts for rationalizing interfaces formed during phase nucleation and growth. Structurally different and confined in space, metastable interfaces occurring during polymorph transformations bring about distinct diffusion behaviour of the chemical species involved. More generally, stable structures emerge as a result of the concurrence of the
transformation mechanism and of chemical reactions within the phase-growth fronts.

References

1. D. Zahn, S. Leoni, Phys. Rev. Lett. 2004, 92, 250201.
2. S. Leoni, D. Zahn, Z. Kristallogr. 2004, 219, 345.
3. D. Zahn, O. Hochrein, S. Leoni, Phys. Rev. B 2005, 72, 94106
4. D. Zahn, Yu. Grin, S. Leoni, Phys. Rev. B 2005, 72, 64110
5. D. Zahn, O. Hochrein, Yu. Grin, S. Leoni, Phys. Rev. B 2006, 74, 094106
6. S. E. Boulfelfel, D. Zahn, Y. Grin and S. Leoni, Phys. Rev. Lett. 2007, 99, 125505.
7. S. E. Boulfelfel, S. Leoni, Phys. Rev. B 2008, 78, 125204
8. S. Leoni, Chem. Eur. J. 2007, 13, 10022.
9. M. Pasciak, S.E. Boulfelfel, S.Leoni, 2008, submitted to PRL.
10. S. Leoni, R. Ramlau, K. Meier, M. Schmidt, U. Schwarz, PNAS 2008, 105, 19612