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

实验方法和理论方法对电荷密度的研究在材料科学领域变得越来越重要。对于寻找各种陶瓷材料奇特物理性质起源的科学家来说尤其如此。然而，在实验方法中，诸如消光、多次散射、吸收、计数统计和热扩散散射等影响迄今为止限制了实验数据的准确性。最近，我们成功地在筑波高能加速器研究机构的光子工厂使用小晶体获得了几乎无消光的衍射数据。这里报告了许多技术上重要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。虽然对Sr掺杂剂在相变机理中所起的作用进行了探讨。利用x射线衍射和各种模拟技术测量电荷密度，弥补了Sr掺杂对相变影响的结构化学信息的不足。用单晶同步x射线衍射在297K下测定了x约为1/8的La_<2-x>Sr_xCuO_4的电子密度分布，不仅揭示了Cu的d_<x^2-y^2>轨道空穴，而且揭示了Cu具有I4/mmm四方对称的无序性质。分子动力学模拟证实了这些局部结构紊乱。

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.