Structural study of Organic Complexs where Neutral ionic transition occurs

发生中性离子转变的有机配合物的结构研究

基本信息

批准号：
06640445
负责人：
NOGAMI Yoshio
金额：
$ 1.34万
依托单位：
Okayama University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

项目摘要

Using X-ray, we directly observe structural changes associated with temperature and pressure induced neutral-ionic transition (NIT) in tetrathiafulvalene-p-chloranil (TTF-CA) and 2,6-dimethyltetrathiafulvalene-p-chloranil (DMTTF-CA). For TTF-CA,below Tc of 84K,changes in intramolecular bond lengths verified a increment in molecular ionicity from 0.4 (neutral phase) to 0.7 (ionic phase). In ionic (I) phase below 84K,TTF and CA molecules, which were originally located at the inversion center in neutral (N) phase, shift in contrary directions owing to the spin-Peierls instability and form a magnetic singlet dimer with a 3.3% distortion. Three dimensional order of the molecular dimerization changes space group for TTF-CA from P2_1/n (neutral) to Pn (ionic). Owing to absence of the inversion symmetry, Ionic TTF-CA become a organic ferroelectrics.In DMTTF-CA,changes in unit cell parameters, anisotropic temperature factors and bond lengths were observed below the neutral-ionic transition temperature of 65K.These changes indicate, in low temperature phase 1) coexistence of neutral and ionic portions in crystal 2) a increase in molecular ionicity and 3) a molecular dimerization in ionic portion whose amplitude is similar to TTF-CA.The predicted staging superlattice in the N-I coexisting phase was not observed. Taking account of interchain electrostatic interaction together with the lattice parameter variations at low temperature and under pressure, this coexistence can be understood.

使用 X 射线，我们直接观察四硫富瓦烯-对四氯苯醌 (TTF-CA) 和 2,6-二甲基四硫富瓦烯-对四氯苯醌 (DMTTF-CA) 中与温度和压力诱导的中性离子转变 (NIT) 相关的结构变化。对于TTF-CA，在低于84K的Tc下，分子内键长的变化证实了分子离子度从0.4（中性相）增加到0.7（离子相）。在低于84K的离子（I）相中，原本位于中性（N）相反转中心的TTF和CA分子，由于自旋-Peierls不稳定性而向相反方向移动，形成磁性单线态二聚体，磁性单线态二聚体的磁性单线态二聚体的磁性单线态二聚体失真。分子二聚化的三维顺序将 TTF-CA 的空间群从 P2_1/n（中性）更改为 Pn（离子）。由于不存在反演对称性，离子TTF-CA成为有机铁电体。在DMTTF-CA中，在中性离子转变温度65K以下观察到晶胞参数、各向异性温度因子和键长的变化。这些变化表明，在低温阶段 1) 晶体中中性部分和离子部分共存 2) 分子离子性增加 3) 离子部分分子二聚化，其幅度类似于TTF-CA。未观察到预测的 N-I 共存相的分级超晶格。考虑到链间静电相互作用以及低温和压力下晶格参数的变化，这种共存是可以理解的。