Raman Investigation of Alkali-Doped (Ch)x films

Abstract

Resonance Raman spectra induced by (CH)_x films chemically or electrochemically doped with alkali metals are reported. At low doping levels, Raman bands characteristic of the trans isomer are observed. The Raman spectra can be well fitted using the theory developped by Mulazzi based on a bimo-dal distribution of long and short trans segments respectively. At the same time, typical results obtained for a cis-rich (CH)_x sample, as well as its behavior during a thermal isomerization, are recalled in the frame of the Mulazzi model. When the polymer is highly doped with Li (or Na) atoms, new features at ? 1600 cm^?1 and 1270 cm^?1 appear and could be an indication that n-doped films are less disordered than p-doped systems.     

Can Two-Dimensional Fullerene Polymers Be Intercalated?

Abstract

Two-dimensional C₆₀ polymers can be produced by treatment at high T and high p. Attempts have previously been made to intercalate these layered materials by alkali metals using the gas phase method but the polymers have always decomposed. We investigate here whether intercalated 2D polymers can be formed by other methods, such as by polymerization in the presence of alkali metals. Preliminary x-ray and Raman data can be interpreted to indicate the presence of an alkali metal intercalated tetragonal fullerene polymeric structure.     

Synthesis and structural characteristics of carbon aerogels with a high content of Fe,Co, Ni,Cu, and Pd

High content metal carbon aerogels have been prepared by sol–gel polymerization of formaldehyde with potassium salt of 2,4-dihydroxybenzoic acid, followed by K⁺-exchange with Fe(II), Fe(III), Co(II), Ni(II), Cu(II) and Pd(II) ions from an aqueous or acetoneous solution and subsequent supercritical drying with CO₂. Carbonization at 1050 °C, under an inert atmosphere, transforms the metal ion doped organic aerogels into metal and/or metal oxide nanoparticles-doped carbon aerogels. The resulting materials were characterized by means of elemental analysis, nitrogen adsorption, transmission electron microscopy and X-ray diffraction. The structural properties and metal concentration of the doped carbon aerogel depend on the type and valence of the precursor metal salt. The presence of some graphitic nano-ribbons was evidenced in the case of Fe-, Co-, and Ni-doped carbon aerogels.     

Synthesis and characterization of carbon‐doped ZnSn(OH)6 with enhanced photoactivity by hydrothermal method

Well‐dispersed carbon‐doped ZnSn(OH)₆ submicrocubes were successfully synthesized through a facile and economical hydrothermal method at 433K, which used green chemical glucose (C₆H₁₂O₆) as the carbon‐doping source. Photocatalytic activity of the as‐synthesized C‐doped ZnSn(OH)₆ was evaluated by studying photocatalytic decomposition of methylene blue (MB) in aqueous solution under visible light irradiation(≥ 400 nm). The results show that carbon‐doped ZnSn(OH)₆ photocatalysts exhibited higher photocatalytic performance as compared to pure ZnSn(OH)₆. 1.0 wt% C‐doped ZnSn(OH)₆ photocatalyst exhibited obviously higher photocatalytic activity that of pure ZnSn(OH)₆ or other C‐ZnSn(OH)₆ catalysts under the same condition. The enhanced photocatalytic degradation of MB could be attributed to the doping of carbon and the possible mechanism for high photocatalytic activity of C‐doped ZnSn(OH)₆ was discussed.     

Formation and Structure of Cluster-Included Carbon Nanocapsules Prepared by Polymer Pyrolysis

Abstract

Formation of carbon nanocapsules with various clusters (SiC, Au, Fe. Co. Ge. and GeO₂) by polymer pyrolysis was investigated, and nanocapsules with SiC and Au nanoparticles were produced by thermal decomposition of polyvinyl alcohol at ?500°C in Ar gas atmosphere. The formation mechanism of nanocapsules and a structural model for the nanocapsule/SiC interface were proposed. In addition, carbon clusters were formed at the surface of carbon nanocapsules, and carbon onions were produced by electron irradiation of amorphous carbon produced from polyvinyl alcohol. The present work indicates that the pyrolysis of polymer materials with clusters is a useful fabrication method for the mass-production of carbon nanocapsules and onions at low temperatures compared to the ordinaly are discharge method.     

The mixed alkali effect in lithium-sodium borate glasses

The electrical conductivity of a series of 0.35 (Li, Na)₂O·B₂O₃ glasses shows a minimum at the composition Na/(Na+Li)～0.6, which becomes stronger as the temperature is decreased; the activation enthalpy for electrical conductivity shows a maximum at this composition. In general, replacing 1% of the total oxygen concentration by chlorine or bromine (keeping the total alkali content fixed) in these glasses increases the conductivity; fluorine doping has an opposite effect. The mixed alkali effect, expressed in terms of the compositional dependence of the activation enthalpy for conductivity, is enhanced when borate glass is doped with fluorine, but is slightly diminished when doped with chlorine or bromine. The results are explained in terms of the structure of halogenated alkali-borate glasses, and discussed in relation to the origin of the mixed alkali effect.     

Enhancement of stability of growth,structural and NLO properties of KDP crystals due to additive along with seed rotation

Potassium Acetate (CH₃COOK) and Potassium Citrate (K₃C₆H₅O₇) as new additives were added into the potassium dihydrogen phosphate (KDP) solutions in different molar ratios. The metastable zone width and induction period with and without these additives were determined and compared. Dielectric measurements on pure and doped KDP crystals at various temperatures ranging from 313 to 423 K were carried out by the conventional parallel plate capacitor method which results low dielectric constant value dielectrics in doped crystals. The high resolution XRD studies show that CH₃COOK doped KDP crystal and K₃C₆H₅O₇ doped KDP crystal do not contain any internal structural grain boundaries and indicates that the crystalline perfection is very good. Moreover, the addition of these potassium additives improves the quality of the crystal and yields highly transparent crystals with well defined features. The effect of additives on the growth, nucleation kinetics, structural, NLO and optical properties has been investigated. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectroscopic investigation and optical characterization of novel highly thulium doped tellurite glasses

In this paper, optical properties of 75TeO₂-20ZnO-5Na₂O host glass doped with concentration of Tm³⁺ up to 10 %mol were studied in order to assess the most suitable rare earth content for short cavity fiber lasers. Raman spectroscopy revealed a change in the glass structure while increasing Tm³⁺ content, similar to the well known addition of alkali ions in a glass. Influence of the fabrication process on the OH⁻ content was determined by FTIR measurements. Refractive index of Tm³⁺ doped tellurite glasses was measured at five different wavelengths ranging from 533 nm to 1533 nm. Lifetime and emission spectra measurements of the Tm³⁺ doped tellurite glasses are reported.     

Structural studies of solution-made high alkali content borate glasses

The glass forming range of alkali borates has been extended to R = 5.0 (83 mol% alkali oxide) using a solution method. This method involves the reaction between solutions of boric acid (H₃BO₃) and alkali hydroxide (MOH). Physical properties and NMR studies were performed on the intermediate and final glass products of this method. We have obtained results for the entire alkali borate system including lithium, sodium, potassium, rubidium and cesium. The structure of these invert glasses remains enigmatic.     

Resonance Raman Scattering of Br2 Doped Single-Walled Carbon Nanotube Bundles

Abstract

We have measured Raman spectra of bromine doped single-walled carbon nanotubes (SWNTs) using various laser lines to clarify the electronic states of the doped SWNT. In the case of evacuated sample after full doping, two breathing mode peaks were observed simultaneously by visible laser excitations. We assigned the higher frequency peak to the doped SWNT bundles, and the other peak to the undoped portions in the sample. Intensity ratio between them decreased with decreasing excitation energy, and in the infrared region, the breathing mode band of the doped bundle was not observed. These results can be explained by a simple rigid band model.     

Effect of the counter-ion of the basification agent on the pore texture of organic and carbon xerogels

Organic and carbon xerogels were prepared by polycondensation of resorcinol with formaldehyde in water, followed by evaporative drying and, eventually, pyrolysis. The pH of the precursor’s solution was fixed at 6.0 in all cases by adding various hydroxides as basification agent. Three alkali metal hydroxides (LiOH, NaOH and KOH) and three alkaline earth metals hydroxides (Ca(OH)₂, Ba(OH)₂, Sr(OH)₂) were used. It was found that the pore texture of the organic and carbon xerogels is totally independent on the cation size, but depends on the charge and concentration of the counter-cation. Indeed, the pore size of the alkaline earth metal loaded samples is larger than that of the alkali metal-doped xerogels. As a matter of fact, to reach the same initial pH, the concentration in alkali metal hydroxide must be twice that of the alkaline earth metal base. The effect of ions on the pore texture was thus attributed to electrostatic effects on the microphase separation process that occurs prior to gelation.     

Doping of Carbon Nanotubes by Heavy Alkali Metals

Abstract

Multiwall (MWNT) and single wall (SWNT) carbon nanotubes were intercalated with heavy alkali metals. From the point of view of their composition, alkali 2D superlattice, EPR and ¹³C NMR characteristics, the intercalation compounds of MWNT (1^st and ^2nd stage) are close to their parent GIC. An expansion of the 2D triangular lattice of SWNT bundles was clearly detected, showing that the alkali atoms are intercalated in the free space between the tubes.     

Electrical and Optical Properties of Conducting Polymer and Carbons in Nano-Scale Periodic Structure and their Intercalation Effects

Abstract

Nano-scale periodic structures of conducting polymer and carbons, which were prepared by infiltration of polymers and carbons in nano-scale interconnected periodic pores in synthetic opals made of regular array of SiO₂ spheres and then removing SiO₂ by etching, have been found to exhibit novel electrical and optical properties. Their electrical and optical properties in thus fabricated conducting polymer and carbon replicas change drastically upon pyrolysis due to progress of carbonization and graphitization. That is, due to the changes in periodicity, pore size, carbonization degree and crystal structure, electrical conductivity, magnetoconductance and their temperature dependences and optical reflection spectra have changed drastically. These replicas with porous nature can be infiltrated and also intercalated with various materials, resulting in also remarkable changes of properties. The synthetic opal infiltrated with conducting polymer can be electrochemically doped, with which remarkable change of optical properties have been observed due to the shift of the diffraction peak accompanying with the change in refractive index. Alkali metal intercalated carbon and graphite with nano-scale periodic structures have been also studied. The applications of these nano-scale periodic structures of conducting polymer and carbon are also discussed.     

Thermal Expansion and Superconductivity in Alkali Metal- and Silver-doped Bi?Sr?Ca?Cu?O System

Samples with the nominal composition Bi₂Sr₂CaCu₂O_y with na doped at the Ca site and K doped at the Sr site are prepared by solid state reaction method. From the X-ray diffraction data it is found that all the the samples have exhibited a single phase 2212. The D.C. electrical resistivity data show that for Na-doped samples the T_c (zero) varies from 80 K to 85 K and for K-doped samples it is from 79 K to 82 K. The loss of oxygen from these samples around 400°C was confirmed by high temperature dilatometry. The variation of the thermal expansion coefficient (“α”) with temperature for different alkali dopings are discussed. Also the samples with the nominal composition Bi₄Sr₃Ca₃Cu_4−xAg_xO_y (with x = 0, 0.1, 0.2, 0.3) were studied.     

Crystal structure of potassium titanyl phosphate doped with zirconium

This paper reports on the results of precision X-ray structural investigations of single crystals of the compounds KTi_0.96Zr_0.04OPO₄ (at 293 K) and KTi_0.97Zr_0.03OPO₄ (at 293 and 105 K). No significant splitting of the positions occupied by potassium atoms is revealed. This result is in agreement with a considerable decrease in the electrical conductivity of potassium titanyl phosphate KTiOPO₄ (KTP) crystals doped with zirconium (KTP: Zr) as compared to crystals of undoped potassium titanyl phosphate. It is established that the difference between the Ti-O bond lengths in chains formed by titanium octahedra is not a single structural parameter responsible for the nonlinear optical properties of crystals in this series.     

Spectral absorption of tellurium in alkali borate glasses

The spectral absorption of tellurium-containing lithium, sodium and potassium borate glasses in the range of 300–700 nm was used to identify the states of tellurium formed in such glasses. Depending on the nature and concentration of the alkali oxide the glasses obtained were either colourless, rose which is attributed to the formation of the polytelluride ion or grey which is attributed to the formation of elemental tellurium particles. The tellurites and/or tellurates are expected to form in glasses of high content of either Na₂O or K₂O which were colourless. The sequence of formation of the different states of tellurium with increasing alkali content is in accordance with acidity-basicity concept.     

Synthesis of Co‐doped CeO2 nanorods modified glassy carbon electrode for electrochemical detection of nitrobenzene

CeO₂ nanoparticles (CNPs), Co‐doped CeO₂ nanoparticles (CCNPs) and Co‐doped CeO₂ nanorods (CCNRs) were synthesized by simple co‐precipitation method and explored their sensing behaviour towards nitrobenzene. XRD and TEM analysis confirmed the presence of cubic fluorite structure of the CNPs, CCNPs and CCNRs. EDX analysis confirmed the presence of Cobalt in CeO₂ nanorods. The electrochemical sensing of nitrobenzene was carried out using CCNRs‐modified glassy carbon (GC) electrodes by means of cyclic voltammetric (CV) technique. The peak current (I_p) was found to be linearly co‐related to nitrobenzene (NB) concentration (R² = 0.9665). A substantial enhancement in cathodic peak current (C1), and sensitivity (∼738.8 nA/μM) was observed for the CCNRs‐modified GC electrode than those of CNPs and CCNPs‐modified electrodes.     

On the Lead Determination in Alkali Halides by Spectroscopic Method

The octahedral complex [PbX₆]^4- (X=Cl, Br) in natrium/potassium chloride or bromide monocrystals as well as in the concentrated solutions of these alkali halides, impurified by lead, shows a characteristic absorption in the region 250-300 nm. Using the height of this absorption band, a quantitative method for determination of lead in the range 8x10¹⁴ - 3.2x10¹⁶ atoms/cm³ of halide monocrystals or 0.5 - 20 mg/ml of solutions respectively, was elaborated. Standard graphs of the peak extinction of [PbX₆]^4- in natrium/potassium chloride and bromide as function of the lead concentration have been obtained.     

Structure and properties of glasses in the MI + M2S + (0.1Ga2S3 + 0.9GeS2), M = Li, Na, K and Cs, system

The structure and properties of glasses in the MI + M₂S + (0.1Ga₂S₃ + 0.9GeS₂), M = Li, Na, K and Cs, system were studied using Raman, IR spectroscopy, DSC and density measurements to help better understand the ionic transport in these glasses. The glass forming ranges of these ternary glasses were compared to those of the binary alkali sulfide and germanium sulfide systems. The more extensive glass forming range in the Na₂S system was used to examine the more extensive changes of structure and properties of these glasses as a function of Na₂S content. As expected, non-bridging sulfurs (NBS) form with the addition of alkali sulfide. Unlike their oxide counterparts, however, the alkali sulfide doped glasses appear to support longer-range super-structural units. For example, evidence that the adamantine-like structure exists in the K₂S and Cs₂S modified glasses is found in the Raman spectra of the glasses. The structural role of the alkali iodide addition was also explored since the addition of alkali iodide helps to improve the conductivity. For most of these glasses, as observed in many other oxide glasses, the added MI dissolves interstitially into the glass structure network without changing the alkali sulfide network structure. In 0.6Na₂S + 0.4(0.1Ga₂S₃ + 0.9GeS₂) glasses, however, the added NaI may affect the glass structure as it causes systematic changes in the frequency of the Ge-S network mode as seen in the Raman spectra.     

Electrical Conductivity and Crystal Structure of Pure and SrCO3-doped K2CO3

Electrical conductivity of pure and SrCO₃ doped potassium carbonate has been investigated in the temperature range between 350 and 800 °C. Sintered carbonate mixtures were analysed by X-ray powder diffraction techniques at room temperatures. The conductivity of SrCO₃ doped K₂CO₃ increases nearly linear up to 10 mol.% and decreases in the range between 20 and 50 mol.% continously. X-ray diffraction patterns do not show changes up to 10 mol.% SrCO₃ in the host lattice. The compound K₂Sr(CO₃)₂ was found for samples containing 15–50 mol.% SrCO₃. The lattice constants of hexagonal crystals which are isotypic with K₂Ca(CO₃)₂ are a₀ = (534 ± 1) pm and c₀ = (1352 ± 2) pm.