Neutral-ionic phase transition in two-dimensional organic semiconductor

二维有机半导体中的中性-离子相变

基本信息

批准号：
13440088
负责人：
HASEGAWA Tatsuo
金额：
$ 8.06万
依托单位：
National Institute of Advanced Industrial Science and Technology (AIST) (2003)Hokkaido University (2001-2002)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

项目摘要

Valence instability or neutral-ionic (NI) phase transition in molecular semiconductor crystal, (BEDT-TTF)(ClMeTCNQ), is studied. We undertake to explore the new electronic phenomena based on the valence fluctuations around the quantum critical point, by studying the structural, magnetic, and dielectric properties of the compound under pressure and low temperature. The results of this project are summarized as follows;1.Structure analyses:We successfully developed the Be-based high pressure cell (application filed for a patent) for X-ray diffraction measurements under uniaxial pressure and low temperature. With use of this facility, we succeeded in the structural analyses below and above the NI transitions and observed the variation in the crystal symmetry and lattice constants.2.ESR study:By magnetic probe sensitive to the appearance of cation and anion radical 1/2-spins, we directly demonstrated how the NI phase transition develop in (BEDT-TTF)(ClMeTCNQ). By the analyses of the temper … More ature dependence of magnetic susceptibility under pressure, we observed the continuous evolution of the ionic domain fraction through the transition temperature. Particular finding is a presence of the thermoinduced NI meso-phase, where ionic radicals survive even at much higher temperature than the transitions. We conclude that this feature should be the origin of the drastic exponential increase of the magnetic susceptibility at room temperature with application of pressure.3.Dielectric measurements:Enhancement in dielectric response of (BEDT-TTF)(ClMeTCNQ) was observed around quantum critical point of the NI phase transitions. As the enhancement is temperature-and frequency-independent, we conclude that the enhancement should be ascribed to the quantum valence fluctuation between the neutral and ionic phases.We also clarify the mechanism of magneto-lattice phase transitions in (BEDO-TTF)(Cl2TNCQ), which is an isomorphous compound with (BEDT-TTF)(ClMeTCNQ). Furthermore, the research is expanded to the new method for the valence control of molecular semiconductors with use of the FET device structures. Less

研究了分子半导体晶体（BEDT-TTF）（ClMeTCNQ）中的价态不稳定性或中性离子（NI）相变，我们致力于通过研究量子临界点附近的价态涨落来探索新的电子现象。该项目的研究成果如下：1.结构分析：成功研制出X用铍基高压电池（已申请专利）。 -射线利用该装置，我们成功地进行了NI跃迁下方和上方的结构分析，并观察了晶体对称性和晶格常数的变化。2.ESR研究：通过磁探针对Ni跃迁敏感。通过阳离子和阴离子自由基1/2-自旋的出现，我们通过分析(BEDT-TTF)(ClMeTCNQ)的温度依赖性，直接证明了NI相变是如何发展的。在压力下的磁化率中，我们观察到离子域分数在转变温度下的连续演变，特别是热诱导的 NI 中间相的存在，其中离子自由基甚至在比转变温度高得多的温度下也能存活。该特征应该是室温下磁化率随着压力的施加而急剧指数增加的根源。3.介电测量：在量子周围观察到(BEDT-TTF)(ClMeTCNQ)介电响应的增强由于增强与温度和频率无关，我们得出结论，增强应该归因于中性相和离子相之间的量子价涨落。我们还阐明了磁晶格相变的机制。 (BEDO-TTF)(Cl2TNCQ)，它是与(BEDT-TTF)(ClMeTCNQ)的同晶化合物。此外，该研究还扩展到分子价态控制的新方法。使用 FET 器件结构的半导体较少。