Seminar of the Institute of Nanotechnology and Materials Engineering | Faculty of Applied Physics and Mathematics at the Gdańsk University of Technology

Abstract:

Modulated crystalline structures were for a long time discarded because of their complexity but they are more and more encountered in materials science, mineralogy and biology and sometimes associated with the appearance of particular properties. This is the case for materials of low electronic dimensionality exhibiting Charge Density Wave (CDW) instability.

Transition to a CDW state is described by Peierls as the opening of a gap on the Fermi surface of the material leading to the modulation of the electronic density and to a periodic distortion of the atomic network of the compound (i.e. a modulated structure). Therefore, a transition to a CDW state is characterized by the appearance of an anomaly in the properties of electronic transport as well as by the appearance of additional reflections in the X-ray diffraction (XRD) diagram, called satellite reflections.

CDW compounds are thus perfect examples to show the usefulness of complex crystallography to understand physical phenomena. Illustration of this complementarity will be done with the Monophosphate tungsten bronzes family, enabling to study the evolution of CDW in function of the dimensionality of the material.