Seminar organised by CMT

Subject : The gamma-alpha phase transition in cerium as a hidden structural phase transformation

Speaker: Prof. Dr. A.V. Nikolaev, Institute of Physical Chemistry of RAS, 117915, Moscow, Russia

Abstract:

 Usually different crystallographic forms of a same element are distinguished by their crystal space symmetry. In some cases, for example in metallic cerium, there are two well defined thermodynamic phases: gamma and alpha, which apparently have the same face centered cubic lattice. The existence of such twin phases in cerium has become a challenge to the theory and prompted search of a main factor responsible for the difference. In the talk on the basis of theoretical and experimental studies it is advocated that the well known gamma-to-alpha phase transition in cerium is not really isostructural. This finding makes cerium the first element where the symmetry change is driven exclusively by the valence electron degrees of freedom while the atomic centers of mass (cerium nuclei) occupy the face centered cubic positions.

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