Enhancement of analytical techniques of local structures in functional ceramic materials using synchrotron X-rays

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Both experimental and theoretical approaches to charge density studies have become increasingly important in the field of materials science. This is especially true for scientists seeking the origin of exotic physical properties of various ceramic materials. In the experimental approach, however, effects such as extinction, multiple scattering, absorption, counting statistics, and thermal diffuse scattering, have so far limited the accuracy of the experimental data. Recently we succeeded in the acquisition of virtually extinction-free diffraction data using small crystals at Photon Factory, High Energy Accelerator Research Organization in Tsukuba. Case studies are reported here for many technologically important compounds. One of our concerns was the K_2NiF_4-type structural family. Although about the role played by the Sr dopant in the phase transition mechanism. The present research redeems the lack of structural chemistry information about the effect of Sr doping on the phase transition from the charge density measurement by X-ray diffraction and various simulation techniques. The electron density distribution of La_<2-x>Sr_xCuO_4 with x approximately equal 1/8 determined at 297K using single-crystal synchrotron X-ray diffraction revealed not only the d_<x^2-y^2> orbital hole of Cu but also the disordered nature with tetragonal I4/mmm symmetry. These local structural disorders were confirmed by the molecular dynamics simulations.