Date/Time
Date(s) - 14/04/2008
2:30 pm - 3:30 pm

Title: Atomic Structure at the Nanoscale: A 21st Century Materials Challenge

Speaker: Dr. Dr. Emil Bozin

Institute: Michigan State University

Location: ABB 165

Description:

Study of structure began almost 100 years ago with the pioneering experiments of the Braggs and von Laue. What is there still to be learned in the 21st century? Atomic structure determines physical properties of complex functional materials. Detailed knowledge of the structure is a prerequisite for understanding the physics of these materials. However, in many of these systems structural features of interest are not long range ordered, but exhibit short range order, typically on a nanometer lengthscale. Conventional crystallographic approach used for studying average crystal structure fails at the nanoscale, as significant component of scattering from such “nanophase” materials is diffuse. The atomic pair distribution function (PDF) analysis based on neutron and x ray total scattering experiments, utilizing both Bragg and diffuse scattering, is a powerful tool for assessing the nanometer lengthscale structural information in such complex materials. At Michigan State University we have been developing and applying the PDF method to problems of scientific and technological interest, from nanostructured bulk materials, via nanoporous materials, to nanoparticles. For example, we characterize the structural distortions associated with the local polaronic state of the La1 xCaxMnO3 colossal magnetoresistive manganites above the metal insulator transition [1], and show the existence of locally correlated spin dimer states in CuIr2S4 thiospinel that are not evident in crystallographic measurements [2]. These insights, gained from going beyond the average structure, give key input that will direct complex materials design and synthesis into the future.