手性配体诱导合成分子基铁电材料及其性质研究

Ferroelectric materials are of importance and interest in both fundamental scientific research and various technological applications. Ferroelectrics may be defined as materials which show a spontaneous electric polarization and whose direction of the polarization can be reversed by an electric field. Synthesis of new ferroelectric materials is particularly challenging due to the strict requirements that a compound needs to crystallize in chiral space groups belonging to one of 10 polar point groups. The homochiral compounds should be good candidates, which easily crystallize in chiral point groups with residual dipole moments leading to ferroelectric. In this research, we expect to obtain ferroelectric compounds crystalling in 10 polar point groups by using suitable chiral ligands and metal ions. As to those compounds which don't crystallized in 10 polar point groups, we can search the ferroelectric phase at varied temperature under the Landau theory of phase transitions. Crystal structure of ferroelectric phase and paraelectric phase is determined by variable-temperature single-crystal X-ray diffraction. The effect of the chiral of ligands, metal ion, ligand types and hydrogen bonds on the material ferroelectric property will be discussed and the key influencing fators to material ferroelectric property should be confirmed. The rule of the correlation between the material structural characteristics and their ferroelectric properties will be revealed based on first principle method of the density functional theroy (DFT).

铁电材料作为一类重要的功能材料，在许多技术领域都有着重要的应用。铁电性跟晶体结构有着密切的关系，只有结晶于十个极性点群的晶体，才可能具有铁电性。本项目拟通过引入合适的手性配体与中心金属离子配位，诱导配合物结晶在十个极性的点群中，这样就大大增加了晶体具有铁电性质的可能；对于没有落在具有铁电性质十个极性点群的化合物，可以在朗道相变理论的指导下，通过改变晶体的温度来进一步寻找其铁电相。利用变温X射线单晶衍射仪确定铁电材料在铁电相和顺电相的分子结构，并结合对材料铁电、介电性质的测定，探讨有机配体的手性、构成骨架主体的金属离子和配体的种类、氢键作用等对材料铁电性能的影响，寻找影响材料铁电性能的关键因素；在实验研究基础上，结合基于第一性原理的模拟方法揭示材料结构特征与其铁电性能之间关联性的规律。

本项目基于铁电性跟晶体结构有着密切的关系，只有结晶于十个极性点群的晶体，才可能具有铁电性。手性配体更易诱导化合物结晶在具有铁电性质的十个点群中。通过引入手性哌嗪、手性哌嗪衍生物及手性氨基酸衍生物等手性配体与中心金属离子配位，诱导配合物结晶在十个极性的点群中，并找到了7个具有铁电性质的化合物。利用单晶衍射仪确定铁电材料在铁电相分子结构，并结合对材料铁电、介电性质的测定，探讨有机配体的手性、构成骨架主体的金属离子和配体的种类、氢键作用等对材料铁电性能的影响。对于没有落在具有铁电性质十个极性点群的化合物，根据朗道相变理论，在一般情况下，低温相的对称性较低，高温相的对称性较高。高温相的某些对称元素在低温相不复存在，即失去了某些对称元素，这称为对称性破缺(symmetry breaking)。因此对于没有落在具有铁电性质十个极性点群的化合物，通过改变晶体的温度来进一步寻找其铁电相，得到了了8个具有相变的化合物。