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

在材料科学领域，电荷密度研究的实验和理论方法都变得越来越重要。对于寻求各种陶瓷材料奇异物理特性来源的科学家来说，这一点尤其正确。然而，在实验方法中，消光、多次散射、吸收、计数统计和热扩散散射等影响到目前为止限制了实验数据的准确性。最近，我们在筑波的高能加速器研究机构光子工厂成功地使用小晶体获得了几乎无消光的衍射数据。这里报道了许多具有重要技术意义的化合物的案例研究。我们关注的一个问题是K_2NiF_4型结构家族。虽然关于锶掺杂在相变机制中所起的作用。本研究通过X射线衍射法测量电荷密度和各种模拟技术弥补了有关掺锶对相变影响的结构化学信息的缺乏。用单晶同步辐射X射线衍射法在297K测量了x约等于1/8的La_&lt；2-x&gt；SrxCuO_4的电子密度分布，不仅揭示了铜的d_&lt；x^2-y^2&gt；轨道空穴，而且揭示了具有四方I4/mmm对称性的无序性质。分子动力学模拟证实了这些局部结构的无序。

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.