Neutral-Ionic Phase Transition in Organic Crystals and Thin Films

有机晶体和薄膜中的中性离子相变

• 批准号: 62460026
• 负责人: KOSHIHARA Shin-ya
• 金额: $ 4.29万
• 依托单位: University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (B)
• 财政年份: 1987
• 资助国家: 日本
• 起止时间: 1987 至 1988
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-62460026/
• 关键词: neutral-ionic(NI) phase transition; organic charge-transfer(CT) compound; negative resistance effect; charged soliton; NI domain wall; photo-induced effect; 負性抵抗特性; 光誘起スペクトル; 中性-イオン性転移; 負性抵抗スイッチング現象; NIドメイン壁; 光励起; 非線形誘電応答; 中性ーイオン性転移; 電荷移動錯体

The neutral-ionic (NI) phase transition in organic mixed-stack charge-transfer (CT) coupounds, that is the valence change from the neutral DA to ionic DA stack, has been investigated with particular emphaisis on its dynamical aspect. First, the anomalous charge-transport properties associated with the NI transition have been revealed, which are, for example, expontial increase of conductivity with hydrostatic pressure and strong nonlinear field-dependence followed by the negative resistance effect. The latter effect leads to the current switching phenomena with the temperature-dependent hysteresis loop, when an appropriate load resister is connected in series to the sample. These effects are considered to be correlated with the dynamics of low-energy excitations, such as charged solitons and NI domain walls, characteristic of the coumpound near the N-I phase boundary. Dynamical response was further pursued by measurements of frequency-dependent dielectric constant as well as photo-induced reflectance change near the NI phase transition temperature. The relaxation time of dielectric constant show the thermally activated behaviour with well-defined activation enrgy, which nearly coincides with that for charge transport. The dielectric constant, which is very large (>10^4) for the low dc field, show the strong nonlinearity at temperatures near the NI phase transition. These results indicate that the confined NI domain wall-pairs are responsible for such an anomalous dielectric respnse and the dissociation of these charged pair play an important role in nonlinear transport. The large photo-induced signal could be detected in the I phase where the DA stacks are dimerized due to the spin-lattice interaction. The trasient response and photoinduced spectral change can be interpreted in terms of the photo-injection of NI domain walls into the dimerized ionic DA stack.

有机混合堆电荷转移 (CT) 化合物中的中性离子 (NI) 相变，即从中性 DA 到离子 DA 堆的价态变化，已得到研究，特别强调其动力学方面。首先，揭示了与 NI 跃迁相关的反常电荷传输特性，例如，电导率随静水压力呈指数增加，以及强非线性场依赖性以及随后的负电阻效应。当适当的负载电阻串联到样品时，后一种效应会导致具有与温度相关的磁滞回线的电流开关现象。这些效应被认为与低能激发的动力学相关，例如带电孤子和 NI 畴壁，这是 N-I 相边界附近化合物的特征。通过测量与频率相关的介电常数以及接近 NI 相变温度的光致反射率变化，进一步探究动态响应。介电常数的弛豫时间显示了具有明确激活能的热激活行为，这与电荷传输的行为几乎一致。对于低直流场，介电常数非常大（>10^4），在接近 NI 相变的温度下表现出很强的非线性。这些结果表明，受限的 NI 畴壁对是造成这种异常介电响应的原因，并且这些带电对的解离在非线性传输中发挥着重要作用。大的光诱导信号可以在 I 相中检测到，其中 DA 堆栈由于自旋晶格相互作用而二聚化。瞬态响应和光致光谱变化可以用 NI 域壁光注入二聚离子 DA 堆栈来解释。

项目成果

K.Takaoka;Y.Kaneko;H.Okamoto;Y.Tokura;T.Koda;T.Mitani;G.Saito: Phys.Rev.B. 36. 3884-3887 (1987)

K.Takaoka；Y.Kaneko；H.Okamoto；Y.Tokura；T.Koda；T.Mitani；G.Saito：Phys.Rev.B。

H.Okamoto;T.Komatsu;Y.Iwasa;T.Koda;Y.Tokura;S.Koshihara;T.Mitani;G.Saito: Synthetic Metals. 27. B189-B196 (1988)

H.Okamoto；T.Komatsu；Y.Iwasa；T.Koda；Y.Tokura；S.Koshihara；T.Mitani；G.Saito：合成金属。

Y,Iwasa;T.Koda;S.Koshihara;Y.Tokura;N.Iwasawa;G.Saito: Phys.Rev.B.

Y，Iwasa；T.Koda；S.Koshihara；Y.Tokura；N.Iwasawa；G.Saito：Phys.Rev.B。

H.Okamoto;T.Koda;Y.Tokura;T.Mitani;G.Saito: Phys.RevB,.

H.Okamoto；T.Koda；Y.Tokura；T.Mitani；G.Saito：Phys.RevB，。

T.Mitani;Y.Kaneko;S.Tanuma;Y.Tokura;T.Koda;G.Saito: Phys.Rev.B. 35. 427-429 (1987)

T.Mitani；Y.Kaneko；S.Tanuma；Y.Tokura；T.Koda；G.Saito：Phys.Rev.B。