Proton NMR studies of the structure of trans-(CH)x

The proton NMR line width in undoped and AsF₅ doped polyacetylene shows an abrupt change as a function of temperature, indicative of motional narrowing. The characteristic temperature for the onset of narrowing decreases with increasing AsF₅ concentration. The results are discussed in terms of large amplitude librational or translational motions of the trans-(CH)_x chains. The magnitudes obtained for the second moment at temperatures below and above the narrowing transition are used to obtain information on the chain packing of trans-(CH)_x within the three-dimensional crystal structure.     

Charge transport at mid-gap in trans-(CH)x: An electrochemical study

Electrochemical studies demonstrate that ～300 ppm of charge (equal to the number of neutral solitons in undoped $\text{trans}$-(CH)_x) is removed at mid-gap. These charges are transported through the polyacetylene electrode via hopping among states at the center of the energy gap, in agreement with Kivelson's theory. From analysis of the data, we have been able to determine the soliton creation energy, E_s ? 0.5eV, which is in good agreement with the theoretical value, E_s = (2/π)Δ.     

Infrared study of cis-trans isomerization of (CH)x films

Cis-trans isomerization of polyacetylene has been investigated by infrared spectroscopy over the temperature range 115–180°C. It is shown that isomerization is slow at 115°C and becomes rather fast above 140°C. The chemical processes during the isomerization appear to be complex, and a beginning of decomposition occurs above 140°C.     

Dynamic charges for photoexcited defects in trans (CH)x

We show that the dynamic charge for an arbitrary vibrational excitation of a photogenerated defect in (CH)_x vanishes in the SSH Hamiltonian for a band filling which is symmetric with respect to the interchange of electrons and holes. As a consequence solitonic excitons do not contribute to the infrared conductivity although dissociated charged defects do. Trapping of dissociated kinks at defects on the chain is suggested as a pinning mechanism.     

顺式聚乙炔中双极化子的新电子定域态

本文用自洽迭代的方法研究了顺式聚乙炔cis-(CH)_x中双极化子的电子能谱。结果发现,除了禁带中两个在连续模型中存在的深能级电子束缚态外,还存在一些浅能级的电子束缚态。它们形成分立的能级,并分别位于导带的顶部和底部以及价带的顶部和底部。这些电子态的定域程度随着电子晶格耦合参数λ及电子相互作用U的不同而变化。 关键词：     

聚乙炔孤子的二维局域振动模及其键弯曲势的影响

本文考虑了反式聚乙炔的平面结构,在二维空间内研究了孤子的局域振动模,并在此基础上讨论了键弯曲势对孤子局域模的影响,结果发现:1)晶格在垂链方向的振幅与链向的可比拟;2)当耦合参数λ取定值时,产生新的局域模(与SSH模型比较),且局域模的数目随着键弯曲势参数K的增加而增多,其局域性也随之增强。 关键词：     

The electronic properties of [CH(FeCl4)0.061]x

The temperature dependence of d.c. conductivity, thermopower and electron paramagnetic resonance (EPR) results on [CH(FeCl₄)_0.061]_x are reported. The d.c. conductivity and thermopower measurements indicate metallic charge transport along the polyacetylene chain interrupted by the interfibril contact resistances and also ‘dragged’ primarily by the dopant ions. The initial measurements of EPR show Dysonian lineshape with very broad linewidth (ΔH ≈ 600 G at room temperature). The temperature dependence of EPR absorption intensity implies that there exist localized magnetic moments. The observed g value (g ≈ 2.03) suggests the dopant anion is in a form of (FeCl₄)^-.     

Spin diffusion in the nuclear magnetic relaxation of isotopically labelled (CH)x

Isotopically labelled (CH)_x samples have been studied to probe the influence of nuclear spin diffusion on the relaxation mechanisms of polyacetylene. The results are discussed in terms of two spin species: those relaxing by direct interaction with solitons and those diffusing by mutual flip-flop towards this well relaxed core. Predictions are made for the time dependence of magnetization recovery and for the frequency dependence of long T₁.     

Na掺杂反式聚乙炔中的孤子晶格的能谱与电子束缚态

从离散的ＳＳＨ模型出发，考虑了链内的电子相互作用，以及由杂质和周围链上的荷电孤子产生的库仑势的影响，探讨了各种掺杂浓度的反式聚乙炔中孤子晶格的能谱与电子束缚态。计算结果表明：在孤子晶格的能谱中，在价带底有两条定域能级，在导带顶存在着多个电子束缚态，随掺杂浓度的升高，束缚态的局域性减弱，禁带中的孤子能级形成孤子能带。当掺杂浓度高达１６．６７％时，所有的电子束缚态都消失，转变为扩展态。孤子晶格的禁带宽度随着掺杂浓度的增加而增大，最高占据态与导带底之间的能隙则随之逐渐减小。孤子能带底与价带顶之间的能隙在临界浓度附近有一极大值。还讨论了电子－电子相互作用对孤子晶格能谱的影响。 关键词：     

π-electron character observed through the anisotropy in the ENDOR spectra of undoped (CH)x

Electron nuclear double resonance (ENDOR) measurements were performed on stretched films of undoped cis-rich (CH)_x at 77°K. The anisotropy of the hyperfine coupling was directly observed for the first time. The anisotropy shows the π-electron character and is consistent with the assumption of the bond alternation kink in the π-electron system in undoped (CH)_x.     

Raman scattering in brominated (SN)x crystals

Detailed Raman scattering data on brominated (SN)_x crystals ranging in composition from (SNBr_0.27)_x to (SNBr_0.55)_x, and preliminary Raman data on [SN(ICI)_0.125]_x are discussed. The investigation involved a study under various conditions of temperature, pressure and levels of bromination, of the two primary Raman lines at 154 and 230 cm^-1 in brominated (SN)_x, which are polarized along the polymer axis direction. The analysis of the data is consistent with a model in which bromine enters the interfibrillar regions as Br^-₃ and the (SN)_x lattice as Br₂. Infrared data is also presented showing an appreciable decrease in intensity of the SN modes at 995 and 670 cm^-1 on bromination.     

Electrical properties of Na-doped (SN)x single crystal

Electrical resistivity of (SN)_x crystal along the b-axis increases in Na ion solution by several times in a few tens of minutes. Temperature dependence of resistivity and transverse magnetoresistance at 4.2 K in Na-doped (SN)_x do not change remarkably from the pristine (SN)_x. These experimental results are discussed in terms of electron transfer from the dopant (Na) to (SN)_x into consideration, comparing with the case of halogen doping.     

Resonant Raman spectra of deuterated polyacetylene, (CD)x

Raman spectra of films of (CD)_x at 77K show dramatic isotope effects in intensity, as well as pronounced dispersion in band profiles as the excitation wavelength is varied throughout the visible. Long series of overtone lines as well as photoluminescence are seen in spectra of the $\text{cis}$ but not the $\text{trans}$ isomer.     

Anisotropy of interchain interaction in polymeric (SN)x crystals

The technique of polarized reflection microspectroscopy was used to study anisotropy of polymeric sulfur nitride (SN)_x in plasma edge region. The spectra taken from different faces of single crystals indicate the presence of strong anisotropy of interchain interaction due to orientation of the π-electron orbitals and suggest two-dimensional metallic behavior of the π-electron system in (SN)_x.     

Spin dynamics at low temperature in undoped trans-polyacetylene, (CH)x

From dynamical nuclear polarization experiments and ESR lineshape analysis, we show the highly mobile spins, associated with topological solitons, in undoped trans-(CH)_X become gradually trapped and slowed down up on cooling.     

Electrical resistance of epitaxial crystalline films of (SN)x

The electrical resistance of oriented (SN)_x-films has been measured from 300 to 0.07 K. The results indicate a finite intrinsic conductivity in the direction perpendicular to the chains, supporting that (SN)_x is a strong anisotropic conductor rather than a quasi-one-dimensional system.     

热压制备(AgSbTe2)100-x-(GeTe)x合金的热电性能

以Pb粉、Te粉、Ag粉、Ge粉为原材料,在真空气氛下合成(AgSbTe₂)_100-x-(GeTe)_x (x=80---90) (TAGS)合金热电材料, X射线衍射(XRD)分析表明,热压烧结后合金具有低温菱形结构. 通过热压烧结法将TAGS粉末制备成块体材料,运用XRD和扫描电子显微镜对材料的物相成分、 晶体结构和形貌进行了表征.采用直流四探针法测定样品的电导率,当样品两端的温差为1---4℃ 的情况下测量Seebeck系数.通过材料热电性能测试,研究了30---500℃温度范围内不同组分 样品性能参数的变化.结果表明,所制备的TAGS热电材料具有纳米结构, 其性能随着组分的变化而变化, TAGS-80具有较好的热电性能,在530℃时具有最高热电优值(ZT=1.80).     

Direct observation of ‘soliton-like’ spin density distribution in undoped cis-rich (CH)x by ENDOR at 4°K

Electron nuclear double resonance (ENDOR) measurements were performed on stretch oriented undoped cis-rich (CH)_x at 4°K. The presence of the spin density which is comparable with the prediction of the soliton theory was directly observed for the first time. The maximum value of the spin density ranged from 0.11 to 0.19 depending on the choice of McConnell's constant. The form of the spin density distribution was discussed through the analysis of observed anisotropic spectral line shape using a spectrum simulation method.     

Brillouin scattering study of elastic properties of superionic (AgI)x(AgPO3)1−x glasses

Longitudinal and transverse phonon frequencies in superionic (AgI)_x(AgPO₃)_1?x glasses for x = 0.3, 0.4 and 0.5 have been measured by Brillouin scattering. The hypersonic velocities as a function of temperature were determined along with the elastic constants. The velocity data extrapolate linearly to those of α-AgI in support of a local cluster model.     

Brillouin scattering study of elastic anomaly in (KCN)x(KBr)1−x system

Brillouin scattering is used to study concentration and temperature dependence of transverse acoustic phonon frequency ω_TA (110) in (KCN)_x(KBr)_1?x mixed crystals. Unlike pure KCN, mixed xrystals with x < 0.75 show no phase transition upon cooling, however, in these crystals we find a minimum in ω_TA as a function of temperature. This minimum can be understood in terms of dynamical theory of rotation-translation coupling in molecular crystals.