AO4型阴离子无序-有序化诱导的分子铁电材料研究

Research on molecular ferroelectrics is of great significance in the development of ferroelectric materials since they are promising with light, environmental friendly, tunable structures, controllable spontaneous polarization and Curie temperature etc. Compounds containing AO4n-(A = S, P, Cl, Br, As etc, n= 1, 2 or 3) anions may exist a lot kinds of disordered states which varied from one or more disordered oxygen atoms to the whole double or multiple disordered AO4n- anions, even more they can coordinate with other disorder negative ions, positive ions and molecules, which provided a plentiful of resource for the research of molecular ferroelectrics.. In this project, through CCDC data carding, we aim on designing and synthesizing serials of AO4n- anions compounds with rotor-stater type, perovskite type, and inter-layered structures, which can induce the structural phase-transition via the disordered-ordered AO4n- anions. We obtain their structures at different temperatures by X-ray single crystal diffraction, Solid state NMR and PXRD, then analysis the symmetry breaking, reversible structural phase-transition and mechanism of spontaneous polarization, and then judge the space group of ferroelectric state through SHG (second harmonic generation) effect test. Furthermore, we determine their heat and dielectric anomaly by temperatures evolution of DSC (differential scanning calorimetry) and dielectric measurement, and prove the phase-transition temperature, then investigate the impact on structural phase-transition, spontaneous polarization and ferroelctricity from the disorder-order motion of AO4n- anions in host-gust molecules. We hope our study provide some new ideas for the seek of new-type ferroelectrics with high spontaneous polarization value, low dielectric constant and high phase transition temperature.

分子铁电体具有质轻、环保、结构可控、自发强度和相变温度可调等优点，对新型铁电材料发展意义重大。具有无序AO4n-阴离子 (A = S, P，Cl, Br, As等, n= 1, 2, 或 3)化合物繁多，随外界条件变化可能从内部单个、多个氧原子无序到与主客体分子协同无序，为无序-有序型分子铁电体研究提供了新的思路。. 对晶体学数据库研究梳理，构筑系列由AO4n-阴离子无序-有序化诱导结构相变的转子-定子型、钙钛矿型和插层结构的化合物；利用变温X-射线单晶衍射仪、固体NMR等确定不同温度的精细结构，研究其对称性破缺，结构相变和自发极化机理；借助SHG效应判断铁电相空间群的正确性；通过介电、DSC测试仪等表征其随温度变化的介电和热异常行为，确定居里相变温度；揭示AO4n-阴离子无序-有序化运动对结构相变、自发极化和铁电性能的影响，为寻找高自发极化率、低介电常数、高相变温度铁电体提供新途径。

铁电材料在微电子，光伏，传感器，铁电存储器、红外探测器和声表面波等固态器件方面具有非常重要而独特的应用。由于AO4n-阴离子团结构无序表现形式丰富多样，为研究AO4n-型阴离子无序-有序化运动诱导的分子铁电材料研究提供了非常丰富的素材和新的途径。.我们设计合成了5个AO4n-型冠醚包合物如[K2(C12H24O6)]2+·[FeCl4]22-、[H3O+(18-C-6)FeCl4-]和[Habf-(18-crown-6)]+[ClO4]-  (Habf=质子化的4-氨基苯甲酰胺)等，3个有机胺配体和AO4n-型金属阴离子化合物，3个稀土-有机胺化合物，均表现出可逆结构相变行为，其中5个具有铁电性质的化合物；合成了10个ABX3钙钛矿型化合物如[(C4H3S)CH2NH3]2PbX4 ((C4H3S)CH2NH3+ = 2-噻吩甲胺; X= Cl-, Br-, I-)、[R-MPA]2CdCl4，[R-MPA+=(R)-(-)-1-甲基-3-苯基丙胺]等，均具有可逆相变行为，其中4个具有高温相变。化合物[H3O+(18-C-6)FeCl4-]分别在207 K、339 K和372 K均表现出可逆相变行为，其中在207 K至339 K温度区间具有明显的铁电特征，自发极化率达4.15μC/cm2, 这种具有连续相变的分子化合物非常少见；此外我们还发现了一个化合物表现出弛豫性铁电体特征，相变发生在一定的温度区间，且介电常数随频率的增加而增加，对开发介电开关、顺-铁电转换有极为重要的应用，为分子基铁介电材料的发展提供了有效的策略。.研究成果在化学类知名期刊Appl. Mater. Today.、Chem-Eur. J、Chem. Mater.、Dalton Trans.、Inorg. Chem. Front.、Inorg. Chem.、Chem. Asian J.、J. Mater. Chem. C等期刊上发表了28篇高水平论文，其中影响因子大于3.0的文章15篇；申请人在4年里培养的毕业的11名研究生，有 3 位研究生考上 985 高校的博士生，有3人获省级优秀硕士论文，5人获得江西江西理工大学优秀毕业论文，超额完成了各项考核指标。