新型多晶材料结构与磁结构的中子衍射研究

X-ray and neutron diffractions are two essential probes for the structure study. Their combined application in condensed-matter research has led to outstanding worldwide breakthroughs in recent years. This research program takes advantage of, on the neutron side, the keen sensitivity to light elements and the high contrast in resolving different elements. On the chemistry side, from the preparation of novel crystalline compounds, we determine their initial structural model by X-ray, electron-microscopy, and other characterization, and then perform the neutron powder diffraction, to get the accurate atomic coordinates and site occupancy of all the elements by Rietveld refinement, thus achieving a full crystallographic structure. According to the magnetic properties such the magnetic susceptibility data of the compounds, temperature-variable neutron diffraction experiments are taken for the further invetigations of magnetic structures. Magnetic ordering will manifest itself with new magnetic reflections and/or superimposed intensity at the nuclear Bragg peaks. The information regarding the crystal and magnetic structures will be correlated with the data of the chemical and magnetic behavior of the samples, which will shed light into understanding the relationship between the crystal/magnetic structures and the chemical/magnetic behavior of the materials. The methodology of structural refinement by neutron data or its combination with X-ray for probing the structures of solid state compounds, and learning the ordered magnetic structures will be established. The overall result will in principle provide guidance or even a prediction for us to design and prepare future materials that have tailored functionalities.

X-射线和中子衍射是结构研究中最基本的两种方法，将二者结合起来用于凝聚态物质的探索，近年来取得了多项令人瞩目的进展。本项目将从新材料的合成出发，在X-射线衍射等方法确定晶体结构模型的基础上，进一步收集中子衍射数据，利用Rietveld精修确定所有元素的准确位置和占有率；根据磁性质随温度的变化情况，确定中子衍射的温度范围，观察磁有序而导致的新的衍射峰和原有衍射峰强度的变化情况，开展磁有序结构的研究；综合分析晶体结构和磁结构数据与材料的物理化学性质特别是磁性变化特点，理解结构与性能之间的关系。通过本项目的研究，将建立粉末X射线与中子衍射确定新型固体材料结构的解析方案，了解磁结构排布的微观机制，探讨结构与功能关系，为新型功能材料的设计合成提供指导。

按照申请书提出的计划，开展新型无机化合物的合成、结构与性能的研究工作。重点利用粉末X射线结合中子衍射数据、依据Rietveld方法进行晶体结构分析。在如下三个体系取得进展：1）复合氧化物功能材料体系；2）新型分子筛及相关层状硅酸盐前驱体；3）其他相关的材料——稀土卤氧化物的上转化发光、多硼酸盐发光体系等。通过合成策略的调整，得到了十多种新结构的化合物，根据不同体系的特点，研究了其磁学、发光、吸附等性能。对于含有未成对电子离子的体系，在确定晶体结构模型的基础上，根据磁性质随温度的变化情况，收集中子衍射数据，开展磁结构的研究。综合分析晶体结构和磁结构特征，探讨结构与材料的性质的关系。