Magnetic-resonance studies in undoped trans -polyacetylene ( CH ) x . II
Magnetic-resonance studies in undoped trans -polyacetylene ( CH ) x . II
复制标题
未掺杂反式聚乙炔(CH) x 的磁共振研究。
DOI：
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发表时间：
1983
期刊：
影响因子：
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通讯作者：
K. Holczer
中科院分区：
文献类型：
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作者：
M. Nechtschein;F. Devreux;F. Genoud;M. Guglielmi;K. Holczer
报告并分析了未掺杂反式-${(mathrm{CH})}_{x}$ 中的磁共振数据，包括 300char22{}4.2 K 温度范围内的核弛豫时间 (${T}_{1}$) 测量值与频率和 ESR 线宽的关系。结果通过高度一维扩散自旋进行了全面解释，这种扩散自旋可以在存在杂质或缺陷的情况下被捕获，特别是与氧污染有关的杂质或缺陷。扩散自旋的平均数量，由热平衡时的扩散自旋布居数给出，是通过两个参数的温度函数：俘获位点浓度和俘获能量。对于真空密封的样品和空气污染的样品，捕获位点浓度分别为 5% 和 25%。我们发现捕获能量从链到链的分布范围是从最大值${E}_{0}ensuremath{simeq}0.06$ eV（这可能对应于最靠近原纤维表面${mathrm{O}}_{2}$杂质的链）到远在原纤维内部的链的大约零。正如自旋动力学研究所反映的那样，随着温度降低，会发生两种效应。首先，由于俘获效应，扩散态的自旋越来越少。其次，扩散系数降低。从室温值 $mathcal{D}ensuremath{sim}5ifmmode imeselse exttimesfi{}{10}^{ensuremath{-}3}$ ${mathrm{cm}}^{2}$/s 开始，首先下降缓慢，然后对于 $Tl100$ K 似乎遵循幂律 $ensuremath{propto}{T}^{2}$，与 Wada 和 Wada 得出的理论结果类似施里弗在两个声子过程中域壁布朗运动的情况下。自旋离域已针对来自 ESR 的俘获态和来自 ${T}_{1}$ 的扩散态进行了评估。在这两种情况下，都发现自旋密度离域超过 10 到 17 CH 单位。只要考虑到捕获效应，从 trans-${(mathrm{CH})}_{x}$ 中的自旋确定的所有特征和性质都与 solitonchar22{}键交替缺陷char22{}图片一致。
Magnetic-resonance data in undoped trans-${(mathrm{CH})}_{x}$, including nuclear relaxation time (${T}_{1}$) measurements versus frequency and ESR linewidth in the temperature range 300char22{}4.2 K, are reported and analyzed. The results are comprehensively explained in terms of highly-one-dimensional diffusive spins which can be trapped in the presence of impurities, or defects, in particular those connected to oxygen contamination. The average number of diffusive spins, as given by the diffusive-spin population at thermal equilibrium, is a function of temperature through two parameters: the trap-site concentration and the trapping energy. Trap-site concentrations of 5% and 25% have been obtained for samples sealed under vacuum and air-contaminated samples, respectively. The trapping energy is found to be distributed, from chain to chain, from a maximum value ${E}_{0}ensuremath{simeq}0.06$ eV, which likely corresponds to the chain nearest to ${mathrm{O}}_{2}$ impurities located at the fibril surface, to about zero for chains far inside the fibril. As the temperature decreases two effects take place, as reflected by the spin-dynamics studies. First, due to the trapping effect, there are fewer and fewer spins in the diffusive state. Second, the diffusion coefficient decreases. Starting from the room-temperature value $mathcal{D}ensuremath{sim}5ifmmode imeselse exttimesfi{}{10}^{ensuremath{-}3}$ ${mathrm{cm}}^{2}$/s, the decrease is slow at first then for $Tl100$ K seems to obey a power law $ensuremath{propto}{T}^{2}$, similarly to a theoretical result derived by Wada and Schrieffer in the case of Brownian motion of domain walls upon two phonon processes. The spin delocalization has been evaluated for the trapped state from ESR, and for the diffusive state from ${T}_{1}$. In both cases the spin density has been found to be delocalized over 10 to 17 CH units. All characteristics and properties determined from the spins in trans-${(mathrm{CH})}_{x}$ are consistent with the solitonchar22{}bond-alternation defectchar22{}picture, provided that the trapping effect is taken into account.