Infrared and Raman studies of the phase transition in the organic conductor (TTM-TTP)I3

We report the polarized IR reflectance as well as Raman scattering investigations of the organic charge transfer salt (TTM-TTP)I₃ as a function of temperature, below and above the metal–insulator phase transition at T = 160 K. The IR reflectance was measured in the frequency region from 600 to 10,000 cm⁻¹, for the electrical vector of the polarized light parallel and perpendicular to the TTM-TTP stacking axis. For the polarization parallel to stacks the IR spectra are typical for semiconducting charge transfer salts. The electronic part of IR spectra was analysed in terms of a Lorentz model and temperature dependence of the optical transport parameters was determined. For the polarization perpendicular to the stacks we observed two electronic bands at about 5000 and 8000 cm⁻¹. The phase transition at 160 K has nearly no influence on the IR spectrum. The Raman scattering for different excitations (λ = 514.5, 632.6 and 785 nm) was mainly studied within the region of CC stretching vibrations. In this frequency range, three Raman lines at 1426, 1453 and 1486 cm⁻¹ attributed to TTM-TTP molecules are observed. Below 160 K a splitting of the band 1486 cm⁻¹ into two peaks at about 1488 and 1498 cm⁻¹ is found. The intensity and temperature behaviour of the split band at 1498 cm⁻¹ is strongly dependent on sample. The observed spectral modifications are related to an asymmetric deformation of TTM-TTP. Taking into account temperature dependence of bands attributed to the CH stretching and SCH₃ bending vibrations, we suggest that the TTM-TTP deformation can exist also above the phase transition temperature. Above 160 K molecules fluctuate between distorted and symmetrical state forming non-stable domains (pre-transitional effects), but below 160 K the molecular distortion and domains are stable. The existence of electronic band at 5000 cm⁻¹ for the polarization perpendicular to TTM-TTP supports this picture.     

Infrared and Raman studies of the radical anion of α,ω-diphenyl-1,3,5,7,9-decapentaene as a model compound in polyacetylene

The FT-infrared (IR) and Raman spectra of the radical anion of α,ω-diphenyl-1,3,5,7,9-decapentaene (DP₁₀⁻), a polyene molecule with five conjugated CC bonds, were observed in vacuum condition. The IR absorption spectrum for ionic species of polyene molecule was observed for the first time in the experimental method. The CC stretching band of IR absorption has the weak at 1591–1603 cm⁻¹, while the Raman band has the two intense peaks at 1533 and 1574 cm⁻¹. In IR absorption, the in-plane CH bending has the several strong bands between 1448 and 1551 cm⁻¹, whereas the Raman has a strong band used as a marker of negatively charged polyene at 1272 cm⁻¹. The origin of IR and Raman spectra of DP₁₀⁻ is discussed in terms of a polaron model compound in polyacetylene.     

Spectroscopic studies of the radical cation salt (BEDT-TTF)2Pt(NO2)4

We report on spectroscopic studies of the charge transfer salt formed by the organic donor bis(ethelenedithio)tetrathiafulvalene (BEDT-TTF) and [Pt(NO₂)₄]²⁻ anions. In this salt BEDT-TTF molecules are arranged in well-isolated (BEDT-TTF⁺)₂ dimers. Polarized reflectance spectra of single crystals were measured in the IR region (650–6500 cm⁻¹). Moreover, absorption spectra (400–15,000 cm⁻¹) and FT-NIR Raman spectra of powdered crystals dispersed in KBr pellets were recorded. Vibrational and electronic features are discussed. We suggest that the frequency of the CC stretching ν₃(a_g) mode depends non-linearly on the degree of ionization of BEDT-TTF.     

Spectral studies of new organic conductors: κ-(BDH-TTP)4Hg3X8, where X = Cl,Br

Raman spectra of single crystals of κ-(BDH-TTP)₄Hg₃X₈, where X = Cl, Br, were recorded in the 250–3000 cm⁻¹ frequency range for two polarizations of incident light. Additionally, the polarized reflectance spectra of the single crystals of the compounds were recorded from 600 to 7000 cm⁻¹ and fitted with the Lorentz model. The ab initio calculations of normal mode frequencies of the neutral BDH-TTP molecule, the BDH-TTP⁺ cation, and mercury-containing anions were performed. The calculations provided the assignment of vibrational modes observed in the experimental spectra. The analysis of the theoretical and the experimental Raman spectra suggests that both salts contain two kinds of donor molecules: differently charged or/and crystallographically independent ones.     

SERS spectroscopy studies on the electrochemical oxidation of single-walled carbon nanotubes in sulfuric acid solutions

Surface-enhanced Raman scattering (SERS) and cyclic voltammetry (CV) were used to investigate oxidation–reduction processes of single-wall carbon nanotube (SWNT) films deposited on Au supports in 0.5 M H₂SO₄ solutions. In the potential range (0; +1000) and (0; +1500) mV versus saturated calomel electrode (SCE), the oxidation–reduction reactions of SWNT films are quasi-reversible and irreversible, respectively. Anodic polarization of SWNT films until +1000 mV versus SCE produced compounds similar to the bisulfate intercalated graphite. Regardless of excitation wavelength, i.e. 1064 or 676.4 nm, variation in the Raman spectra exhibited a decrease in the intensity of the bands associated with the radial breathing mode (RBM) situated in the 120–240 cm⁻¹ spectral range. Also an increase in the intensity of the D band is accompanied an up-shift of this band. A gradual decrease of the Breit–Wigner–Fano component was observed at λ_exc=676.4 nm. Partial restoration of the Raman spectra was achieved by a subsequent alkaline solution treatment. Potentials higher than +1000 mV versus SCE resulted in SWNTs breakage and fragments of different length were formed such as closed-shell fullerene. This was observed in the SERS spectrum by: (i) the disappearance of the RBM band, (ii) the increased D-band shifted to ca. 1330 cm⁻¹ and (iii) the appearance of a new band at 1494 cm⁻¹, frequently observed also in the Raman spectrum of fullerenes on the type C₇₀, C₈₄, C₁₁₉, as well as in its derivative compounds (e.g. C₆₀O, clathrates, etc.). Appearance and increase in the intensity of the Raman band at 1494 cm⁻¹ as result of an anodic polarization of the SWNT film in solution of H₂SO₄ 0.5 M in 1-butanol is a further evidence of the nanotubes breakage.     

Effect of Fenton reagent on the synthesis of polyaniline

Polyaniline has been prepared using Fenton reagent. The in situ visible spectra during the polymerization process show that the polymerization of aniline was carried out through an intermediate at 530 nm. The absorption band of the resulting product, polyaniline, appears at 700 nm. The conductivity of polyaniline prepared using Fenton reagent can reach 1.04×10⁻² S cm⁻¹, which is strongly dependent on the concentrations of FeSO₄, H₂SO₄ and polymerization time. The cyclic voltammogram of polyaniline prepared using Fenton reagent is much different from that of polyaniline prepared normally, and has the good electrochemical reversibility and a fast charge transfer characteristic in the solution with pH 4.0. The FTIR spectrum indicates that no absorption band attributed to N–H stretching vibrations is present in polyaniline.     

Ex situ XANES,XPS and Raman studies of poly(3,4-ethylenedioxythiophene) modified by iron hexacyanoferrate

X-ray (XPS and XANES) and Raman spectra of poly(3,4-ethylenedioxythiophene) (pEDOT) modified by iron hexacyanoferrate (Fehcf) network are presented. XANES studies allowed to postulate an octahedral surrounding of iron atoms in the material and identified nitrogen and carbon atoms as nearest neighbourhoods. XPS measurements reveal iron–nitrogen and iron–carbon bonds, supporting the XANES results. Chemical interaction between sulphur from pEDOT and iron was also evidenced by XPS. Although both methods give proof of Prussian Blue structure inside the polymer, Raman studies did not show any signal typical for CN at about 2160 cm^?1 (ν). However, the presence of Fehcf was confirmed by the stretching vibrations of Fe–N bond at 146 cm^?1 and Fe–CN vibrations at 270 cm^?1. AFM imaging was performed to illustrate the roughness and morphology of the pEDOT/Fehcf surface.     

Dislocation climb in Mo5SiB2 during high-temperature deformation

During high-temperature compression tests on intermetallic Mo₅SiB₂, the dislocation microstructures vary with increasing temperature and strain rate. At 1400 °C, an increasing tendency exists for slip planes to be of an unexpected type (e.g., {143) and {523)) as a function of the decreasing strain rate and increasing strain that originates from a dislocation climb. As the temperature increases to 1600 °C, the internal strain rate of 6.07 × 10^− 3 s^− 1 from the dislocation climb at 4% strain exceeds the applied value of 1.67 × 10^− 3 s^− 1, and thus, the climb mainly controls the plastic strain, as evidenced by a strength that is lower than that at 1200 °C under the same conditions.     

Spectroelectrochemical study on the charging reactions of electrochemically synthesized films from 2-methoxynaphthalene

The charging–discharging reactions (both p- and n-doping) of films made electrochemically synthesized from 2-methoxynaphthalene in two different organic solvents have been studied by in situ Fourier Transform infrared (FTIR) spectroscopy using the attenuated total reflection, ATR, technique and by Raman spectroscopy. Films were made by cyclic voltammetry, CV. These films could be reversible both p- and n-doped. In situ FTIR–ATR measurements were made during charging–discharging of the electrosynthesized film in monomer-free 0.1 M TBAPF₆ solution. The IR spectra of the doped conducting state show infrared active vibrations (IRAV) bands in the region between 1300 and 700 cm⁻¹. The intensity of these bands increase with increasing charging level. In addition to these bands, a broad absorption can be seen in the high wavenumber region (4000–8000 cm⁻¹). The increased absorption is related to the movement of charged carriers in the film upon doping. FTIR data confirms that an electrically conducting conjugated structure with different redox properties and conjugation length was formed after synthesis in the two different electrolytes.     

Laser doping of chromium as a double acceptor in silicon carbide with reduced crystalline damage and nearly all dopants in activated state

Chromium, a p-type dopant, has been incorporated into silicon carbide by laser doping. Secondary ion mass spectrometric data revealed enhanced solid solubility (2.29 × 10¹⁹ cm⁻³ in 6H–SiC and 1.42 × 19¹⁹ cm⁻³ in 4H–SiC), exceeding the equilibrium limit (3 × 10¹⁷ cm⁻³ in 6H–SiC above 2500 °C). The roughness, surface chemistry and crystalline integrity of the doped sample were examined by optical interferometry, energy dispersive X-ray spectrometry and transmission electron microscopy, respectively, and showed no crystalline disorder due to laser heating. Deep-level transient spectroscopy confirmed Cr as a deep-level acceptor with activation energies E_v + 0.80 eV in 4H–SiC and E_v + 0.45 eV in 6H–SiC. The Hall effect measurements showed that the hole concentration (1.942 × 10¹⁹ cm⁻³) is almost twice the average Cr concentration (1 × 10¹⁹ cm⁻³), confirming that almost all of the Cr atoms were completely activated to the double acceptor state by the laser-doping process without requiring any additional annealing step.     

High pressure Raman studies on the structural conformation of oligophenyls

The goal of this combined experimental and computational study is to investigate the structural conformation of oligo(para-phenylenes) in the crystalline phase, in particular the planarity of this type of molecules. To this end we have performed Raman experiments on para-terphenyl and para-quaterphenyl in a pressure range from 0 to 70 kbar and at temperatures from 10 to 300 K. The positions and the relative intensities of the C–C interring stretch mode at 1280 cm⁻¹ and the C–H in-plane bend mode at 1220 cm⁻¹ have been tracked. We find that upon increasing temperature at ambient pressure the intensity ratio I₁₂₈₀/I₁₂₂₀ drops rapidly at temperatures that coincide with the crystallographic phase transition for the investigated materials. At ambient temperature also, this intensity ratio drops rapidly upon increasing pressure up to about 15 kbar. In the computational part, the Raman frequencies and activities of isolated 3P and 4P molecules were calculated within restricted Hartree–Fock formalism with the interring tilt angles varying from 0 to 90°. These calculations confirm that the I₁₂₈₀/I₁₂₂₀ intensity ratio can be related to the planarity of the molecules. Three-dimensional bandstructure calculations within density functional theory were applied to determine phonon frequencies and estimate Raman activities for the polymer poly(para-phenylene). These simulations show that the same conclusions hold for crystalline environment.     

Effects of surface temperature,flow velocity and ambient pressure on the oxidation of graphite at 1400–2000 °C in O2

The effects of surface temperature (1400–2000 °C), flow velocity gradient (130–600 s⁻¹) and ambient pressure (5–101 kPa) on the oxidation behavior of graphite were studied in O₂. The weight loss rate between 1400 and 1800 °C is independent of the surface temperature but slightly decreases at 2000 °C. Besides, it displays quasi-parabolic increases with increasing the flow velocity gradient and the ambient pressure but levels off above the ambient pressure of 20 kPa. According to the theoretical analysis, the enhancement of the gas-phase CO–O₂ reaction has a joint reduction effect on the weight loss rate.     

Carbazolyl- and diphenylamino substituted fluorenes as hole transport materials

Four fluorene-containing aromatic amines with carbazole and diphenylamine moieties were synthesized by Ullmann coupling. Comparative study on their thermal, optical and photoelectrical properties is presented. One synthesized compound is found to form glass with the glass transition temperature 58 °C as characterized by differential scanning calorimetry. The ionization potentials established by electron photoemission technique are in the range 5.9–6.1 eV. Hole-drift mobilities of 50% solid solution of 2,7-dicarbazolyl-9,9-dihexylfluorene in bisphenol Z polycarbonate established by the xerographic time-of-flight technique exceed 10⁻⁴ cm² V⁻¹ s⁻¹ at electric field of 10⁶ V cm⁻¹.     

Novel thermal protection coating based on Zr0.75Ce0.25O2/phosphate duplex system for polyimide matrix composites fabricated via a combined sol–gel/sealing treatment process

Thermal protection coating based on Zr_0.75Ce_0.25O₂/phosphate system was fabricated on polymer–matrix composites via a combined sol–gel/sealing treatment process. Phosphates sealed the cracks and enhanced the adhesion property via chemical bonding and binding. The Zr_0.75Ce_0.25O₂/phosphate duplex coating exhibited good thermal shock resistance and improved thermal oxidation resistance of the substrate. Due to the protection of the duplex coating, the weight loss of the specimen reduced from (4.83 ± 0.12)% to (0.98 ± 0.08)% and the mass ablation rate decreased from 0.088 ± 0.002 mg cm⁻² s⁻¹ to 0.018 ± 0.002 mg cm⁻² s⁻¹ when testing at 810 °C. Coating failure was attributed to the formation of cracks and delamination.     

Raman study of κ-ET2Cu[N(CN)2]Cl at ambient and ∼300 bars pressures

Anomalies in the temperature dependence of the 246 and 258 cm⁻¹ Raman active phonons below the antiferromagnetic phase transition are reported in κ-ET₂Cu[N(CN)₂]Cl at ambient pressure and are compared to measurements under ∼300 bars that render the compound superconducting. At ambient pressure, due to the Mott-gap opening and/or to the spin–lattice interaction and exchange-phonon modulation, frequency softenings, enhanced intensities and linewidths narrowings of these modes occur at low temperatures.     

Synthesis,characterization and evaluation of cation-ordered LnBaCo2O5+δ as materials of oxygen permeation membranes and cathodes of SOFCs

LnBaCo₂O_5+δ (Ln = La, Pr, Nd, Sm, Gd, and Y) was synthesized via an EDTA–citrate complexing process. The particular Ln³⁺ dopant had a significant effect on the oxide’s phase structure/stability, oxygen content, electrical conductivity, oxygen permeability, and cathode performance. Stable, cation-ordered oxides with layered lattice structures were obtained with medium-sized Ln³⁺ ions over a wide range of oxygen partial pressures, a property essential for applications as oxygen separation membranes and solid oxide fuel cell (SOFC) cathodes. PrBaCo₂O_5+δ demonstrated the highest oxygen flux (∼5.09 × 10⁻⁷ mol cm⁻² s⁻¹ at 900 °C), but this value was still significantly lower than that of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ perovskite (∼3.1 × 10⁻⁶ mol cm⁻² s⁻¹ at 900 °C). The observed difference was attributed to the much longer diffusion distance through a polycrystalline membrane with a layered lattice structure than through cubic perovskite because bulk diffusion was the rate-limiting step of permeation. An area-specific resistance of ∼0.213 Ω cm² was achieved at 600 °C with a PrBaCo₂O_5+δ cathode, suggesting that the layer-structured oxides were promising alternatives to ceramic membranes for SOFC cathodes.     

Electrical properties,sintering and thermal expansion behavior of composite ceramic interconnecting materials,La0.7Ca0.3CrO3−δ/Y0.2Ce0.8O1.9 for SOFCs

This paper presents a high-performance interconnect ceramic for solid oxide fuel cells (SOFCs), based on a modification of La_0.7Ca_0.3CrO_3−δ (LCC). It was found that addition of a small amount of YDC (Y_0.2Ce_0.8O_1.9) into LCC dramatically increased the electrical conductivity. For the best system, LCC + 3 wt.% YDC, the electrical conductivity reached 104.8 S cm⁻¹ at 800 °C in air. The electrical conductivity of the specimen with 2 wt.% YDC in H₂ at 800 °C was 5.9 S cm⁻¹. With the increase of YDC content, the relative density increased, reaching 97.6% when the YDC content was 10 wt.%. The average coefficient of thermal expansion (CTE) at 30–1000 °C in air increased with YDC content, ranging from 11.12 × 10⁻⁶ K⁻¹ to 15.34 × 10⁻⁶ K⁻¹. The oxygen permeation measurement illustrated a negligible oxygen ionic conduction, indicating that it is still an electronically conducting ceramic. Therefore, it is a very promising interconnecting ceramic for SOFCs.     

Top-seeded solution growth and characterization of rhombohedral PMN–30PT piezoelectric single crystals

Piezoelectric single crystals from 70Pb(Mg_1/3Nb_2/3)O₃–30PbTiO₃ solid solution were grown by a top-seeded solution growth method that prevented phase segregation and promoted (0 0 1) growth. Rhombohedral symmetry was confirmed by polarized light microscopy and the dielectric, piezo- and ferro-electric properties were characterized. A dispersive maximum of dielectric permittivity appears around T_C = 125 °C, which slightly shifts towards higher temperatures with increasing frequency, indicating weak relaxor behaviour. Rhombohedral–tetragonal phase transition was detected at 105 °C. This temperature is higher than the depoling temperature of the morphotropic phase boundary compositions (50–80 °C), thus extending the upper limit of the application temperature for electromechanical transducers. The piezoelectric coefficient (d₃₃) was found to be 1240 pC N⁻¹, with a strain level reaching 0.12% at an electric field of 12 kV cm⁻¹. The longitudinal electromechanical coupling factor k₃₃ reaches 85%, which persists upon heating up to 100 °C.     

Highly sinter-active (Mg–Cu)–Zn ferrite nanoparticles prepared by flame spray synthesis

Nanoscale ZnFe₂O₄, Mg_0.5Zn_0.5Fe₂O₄ and Mg_0.2Cu_0.2Zn_0.62Fe_1.98O_3.99 powders were prepared for the first time by flame spray synthesis (FSS). Solutions of metal β-diketonates in organic solvents were used as precursor. Crystalline particles of spinel structure with 6–13 nm primary particle size resulted from the flame process. Particle and crystallite size depended on the flow rate of the atomizing gas, the precursor and its molarity. Compacts prepared from Mg–Cu–Zn ferrite nanoparticles revealed an extremely high sinter-activity. A sintered density of 5.05 g cm⁻³ was achieved after firing for 2 h at 900 °C without any sintering additives, while a maximum density of 4.91 g cm⁻³ was obtained with particles from the conventional ceramic route. The permeability of the sintered Mg–Cu–Zn ferrite nanopowder compacts reached μ = 600 at 1 MHz and the saturation magnetisation was 80 emu g⁻¹. The outstanding sintering activity of the flame-made ferrite powders is attributed to their small primary particle size.     

Characterization of CsC24 prepared from carbon materials with different graphitization degree

Samples of CsC₂₄ were prepared from carbon materials (derived from petroleum cokes) with different graphitization degree and were characterized by X-ray diffraction (XRD), electron spin resonance (ESR) and Raman spectroscopy. The XRD measurement showed that all the host carbon samples heat treated from 1300 to 2800°C being contacted with CsC₈ planar specimen allowed the intercalation of Cs. Correspondingly, the resulting CsC₂₄ samples were able to sorb hydrogen molecules, which is a clear evidence of the formation of the nanospace. The broad ESR signal due to conduction electron observed for carbon samples (heat-treatment temperature, HTT above 2200°C) disappeared after intercalation of Cs because of the spin–orbit interaction caused by the intercalated Cs. The Raman G-band of the CsC₂₄ samples (HTT above 1750°C) shifted from 1584 cm⁻¹ of the host carbon to higher wave number (∼1602 cm⁻¹) in agreement with the reported data for CsC₂₄. In addition, it was confirmed that the D-band signal disappeared for the CsC₂₄ samples (HTT above 2000°C).