9700966 Billinge The local structure of transition metal oxides (TMOs) exhibiting interesting electronic properties will be studied using the pair- distribution function (PDF) analysis of powder diffraction data. This technique utilizes Bragg and diffuse scattering over a very wide range of momentum transfer (Q) and yields the atomic short-range order directly. It goes beyond the approximation of perfect crystallinity and allows the local structure to be solved on length-scales from 1-20 angstroms. This type of structural analysis will be applied to a variety of transition metal oxides such as high-Tc materials, layered manganites and nickelates and the colossal magnetoresistant manganites. In these materials, the structure can respond to the electronic state and we will look for correlations between changes in electrical properties and local structural effects. In this way, the nature of localized electronic states, such as polaronic, bipolaronic and charge-phase-separated states, will be elucidated. %%% The great materials scientist F.C. Franck is reported to have said "crystals are like people -- it is the defects which make them interesting". Indeed, many of the most interesting, and useful, new materials exhibit a high degree of atomic disorder; and it is often the defects which give them their interesting properties. This presents special challenges for solid state physicists and materials scientists because of the difficulty of studying atomic level defects in materials. We will be using the technique of atomic pair- distribution function (PDF) analysis of neutron and x-ray diffraction to characterize transition metal oxides; an important group of materials which fall into the above category. We will use novel data analysis and modeling techniques, developed both by us and by others, to extract quantitative structural information from the data and correlate these observations with the measured electrical properties. A number of these material s show great technological promise, such as the high-Tc superconductors and colossal magnetoresistant manganite materials which may have an application in computer read/write heads for example. We are attempting to understand the role that atomic defects play in their interesting electrical properties. ***
