Condensed Matter Physics Seminar
Structures of Ferroelectrics and Metal-Insulator Transition Systems at the Atomic Scale and the Micro Scale
Many ferroelectric systems have been found to have much different structures at the atomic scale than indicated by conventional x-ray diffraction methods. For example, PbTiO3 above the ferroelectric Curie temperature Tc loses its spontaneous polarization and by x-ray diffraction takes on a cubic structure. But locally it is now known that the Ti site remains displaced from the center of the oxygen octahedron even above Tc. Another surprising result is the recent discovery that, when the (1-x)Pb(Sc,Ta)O3 – x(PbTiO3) ceramic is formed, for x of 5% the local Ti displacement in a PbTiO3 environment is along , not ; the average displacement gradually changes from  to  as x increases to 1. Similarly, there are theories of the metal insulator transition (MIT) system, in which Cr2O3 is doped into V2O3 at the ~ 1% level; such theories suggest that the MIT transforms the material from conducting to insulating at about 0.8% Cr2O3 by the linking up of insulating micro regions so that a percolative transition occurs. At the same time, at the atomic scale the environment of each Cr2O3 site may always be insulating. The experimental data that exit are inadequate to refute or support such models. We have initiated a new DOE funded project to study this problem.
Thursday, October 21, 2004
Gant Science Complex
(The seminar is followed by coffee/tea, cookies, and an informal discussions.)