Seminars Archive
Multiple Bragg Scattering and the Phase Problem. Applications to Quasicrystals and to Resonant Scattering
Abstract
Monday, June 16, 2003, 14:30
Seminar Room, ground floor, Building "T"
Sincrotrone Trieste, Basovizza
Multiple Bragg Scattering and the Phase Problem. Applications
to Quasicrystals and to Resonant Scattering
Roberto Colella
(Purdue University, Physics Department, West Lafayette, U.S.A.)
Abstract
Multiple Bragg Scattering, a situation in which two or more Bragg reflections
are excited at the same time, is a source
of phase information. Applications to quasicrystals will be presented.
The general problem of centrosymmetry, or lack of it,
will be discussed, along with experimental results. Resonant scattering
is a new technique used to get information
about "orbital ordering". The crystal potential gives rise to preferred
orientations of aspherical degenerate orbitals,
responsible for chemical bonding. This is commonly referred to as "orbital
ordering". One of the effects of orbital ordering
is to excite forbidden reflections when the energy of the x-rays corresponds
to an absorption edge. The phases of these forbidden
reflections may be very useful for a complete and accurate description
of orbital ordering. Applications will be shown for Ge and LaMnO3.