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.     

Superconductivity in polymeric sulfur nitride (SN)x at high pressure

Investigations of the pressure dependence of the superconducting transition temperature T_c up to 17 kbar, and of the normal conductivity up to 50 kbar are reported. It is observed that below 8 kbar, the value of T_c increases linearly with the pressure. In addition, there is a significant drop of T_c at about 9 kbar which may be due to a phase transition.     

Optical reflectivity of (SN)x-single crystals

The optical reflectivity of (SN)_x single crystals was measured in the visible region and the near infrared with light polarized parallel and perpendicular to the polymer chain axis. Whereas the reflectivity for light polarized perpendicular to the chain axis is approximately constant in this region, the reflectance for light polarized parallel to the chain axis exhibits a pronounced plasma edge at 2.72 eV. A simple Drude model was used to analyse the data. Differences between these results and those of previous film measurements are discussed.     

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.     

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.     

Temperature dependence of the static magnetic susceptibility of brominated (SN)x

The static magnetic susceptibility of brominated (SN)_x differs markedly from that of the parent material. The conduction electron contribution is increased by a factor of three, and a positive linear temperature dependence is observed in samples with 0.4 Br per SN unit. The magnitudes of both the susceptibility enhancement and the temperature coefficient depend monotonically on bromine content, for concentrations in the range 20–40 atomic %. No simple explanation for this behaviour can be found on the basis of minor perturbations of the properties of the parent material, suggesting that brominated (SN)_x has a band-structure radically altered from that of pristine (SN)_x.     

Nuclear relaxation of the water protons included in (SN)x crystals

The temperature and frequency dependences of the proton spin-lattice relaxation time in H₂O included in (SN)_x crystals have been measured and discussed. It is suggested that a significant amount of water is adsorbed on the surface of the (SN)_x fibers.     

Self-consistent calculation of energy band structure of polysulphur nitride (SN)x, by the intersecting spheres model

It has been shown that the intersecting spheres model gives accurate results when applied to molecules and covalent three dimensional crystals. The model is here used for the calculation of the self consistent electronic structure of single chain of polysulphur nitride. We have also computed the electronic density of states which results in strict agreement with photoemission data.     

Optical properties of orientated (SN)x-films in the visible and near infrared region

Optical reflectance and transmittance measurements between 0.3 and 5.5 eV were performed on (SN)_x-films which showed a parallel orientation of the crystallites with respect to their polymer chain axis.The optical behaviour below 3 eV for light polarized parallel to the chain axis and in particular a strong absorption peak between 1 and 2 eV is explained to be a Maxwell-Garnett resonance of the free carriers. The influence of the free carriers is also observed for light polarized perpendicular to the chains and is analysed by the same model. From the anisotropy of the transport properties the interchain coupling is inferred.     

Raman scattering in (SN)x crystals

Polarized Raman spectra are reported for the high frequency intrachain modes in crystals of the metallic polymer (SN)_x. The principal features observed (at 454, 621, 658 and 782 cm^?1) are strong, very anisotropic, and sharper than in thin films. The strongest feature, at 658 cm^?1, narrows but does not shift with decreasing temperature or increasing pressure. Some of the peaks vary in relative intensity as the laser frequency is varied from 4579 to 6005 Å through the plasma resonance.     

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.     

ESR studies of trans-(CH)x during photoexcitation

A series of spin resonance experiments on samples illuminated with light at photon energies ?ω>E_g are reported. The results set an upper limit on the quantum efficiency for photoproduction of unpaired spins, γ_s? 2×10^-7,implying that the photo-induced excited states and the photo-generated carriers are spinless and are to be associated with charged solitons.     

Anisotropy of electrooptical interaction in LiNbO3 crystals

Results of studying the conditions for optimum electrooptical (EO) interaction in lithium niobate crystals are presented. Analytical formulas are obtained for calculating refractive indices of natural waves and their polarizations for basis X-, Y-, and Z-cuts of crystals for arbitrary orientations of the wave vector of an optical wave. Conditions are found for the appearance of intermode EO interaction causing the orientation of polarization plane of natural waves to become a function of the external electric field.     

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.     

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.     

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.     

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.     

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).     

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)^-.     

Spectroscopic investigation of [(NH4)xK1−x]2SnCl6 mixed crystals

Polycrystalline samples of the solid solution [(NH₄)_xK_1?x]₂SnCl₆(0?x? 1) have been investigated by DSC, X-ray diffraction and Raman scattering experiments. Substitution of K⁺ by NH⁺₄ depresses the phase transition temperature T₁. For 0? x ?0.05 a linear temperature coefficient $\text{d}\text{T}{}_1\text{dx=?5.16}\text{K/mol}$ % is obtained. The cubic lattice constant roughly obeys Vegard's law, whereas the linewidth of the SnCl₆^2?F_2g internal vibration displays a nonlinear dependence on composition.