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，我们直接观察到与温度和压力诱导的中性离子离子过渡（NIT）相关的结构变化（ttff-Ca）和2,6-二甲基trathiaia-fultathiaia-fulthiaia-fulthiaia-fulthiaia-fulvalene-p-氯酸酯（DMTTF-CA）。对于TTF-CA（低于84K）的TTF-CA，分子内键长的变化验证了分子离子性从0.4（中性相）到0.7（离子相）的增量。在低于84K，TTF和Ca分子以下的离子（i）中，最初位于中性（N）相的反转中心，由于自旋 - 旋转不稳定性并形成磁性单二聚体二聚体，其相反方向的变化为3.3％。分子二聚化的三维顺序将TTF-CA的空间群从P2_1/N（中性）变为Pn（离子）。由于不存在反转对称性，离子TTF-Ca成为一种有机铁电。INDMTTF-CA中，单位细胞参数的变化，单位细胞参数的变化，各向异性温度因子和键长的长度和键长在65k的中性离子过渡下的温度下降。离子性和3）离子部分中的分子二聚化，其振幅与TTF-CA相似。未观察到N-I共存阶段的预测分期晶格。考虑到在低温下和压力下的晶格参数变化，可以理解这种共存。