In situ template polymerization of aniline on the surface of negatively charged TiO2 nanoparticles

The in situ oxidative template polymerization of aniline was performed successfully on the surface of negatively charged titania (TiO₂) nanoparticles with a mean diameter of 40 nm using ammonium persulfate and a Chem-Solv solution at pH 1 and 25 °C. SEM showed that the resulting polyaniline (PANI)/TiO₂ composites were well dispersed in solution due to the electrostatic repulsion force. Ultraviolet/visible spectroscopy, thermogravimetric analysis, Fourier-transform infrared spectroscopy, and cyclic voltammetry showed that the optical, thermal, and electrical properties of PANI/TiO₂ composites were quite different from those of pure PANI or TiO₂, which was attributed to the strong interaction between the two components. The conductivity of the PANI/TiO₂ composite was estimated to be 0.91 × 10⁻¹ S/cm at 25 °C in the range of semiconductor.     

Facile synthesis of polyaniline nanofibers using pseudo-high dilution technique

A new approach for the synthesis of polyaniline nanofibers under pseudo-high dilute conditions in aqueous system has been developed. High yield nanoscale polyaniline fibers with 18–110 nm in diameter are readily prepared by a high aniline concentration 0.4 M oxidation polymerization using ammonium persulfate (APS) as an oxidant in the presence of hydrochloric acid (HCl), perchloric acid (HClO₄), (1S)-(+)-10-camphorsulfonic acid (CSA), acidic phosphate PAEG120 (PA120) and sulfuric acid (H₂SO₄) as the dopants. The novel pathway always produces polyaniline nanofibers of tunable diameters, high conductivity (from 10⁰ to 10¹ S/cm) and crystallinity.     

Effect of Cr7C3 on the mechanical, thermal, and electrical properties of Cr2AlC

In this work, phase pure Cr₂AlC and impure Cr₂AlC with Cr₇C₃ have been fabricated to investigate the mechanical, thermal, and electrical properties. The thermal expansion coefficient is determined as 1.25 × 10⁻⁵ K⁻¹ in the temperature range of 25-1200 °C. The thermal conductivity of the Cr₂AlC is 15.73 W/m K when it is measured at 200 °C. With increasing temperature from 25 °C to 900 °C, the electrical conductivity of Cr₂AlC decreases from 1.8 × 10⁶ Ω⁻¹ m⁻¹ to 5.6 × 10⁵ Ω⁻¹ m⁻¹. For the impure phase of Cr₇C₃, it has a strengthening and embrittlement effect on the bulk Cr₂AlC. And the Cr₂AlC with Cr₇C₃ would result in a lower high-temperature thermal expansion coefficient, thermal conductivity, specific heat capacity and electrical conductivity.     

Thermoelectric properties of Bi2SexTe3−x prepared by Bridgman method

Bi₂Se_xTe_3−x crystals with various x values were grown by Bridgman method. The electrical conductivity, σ, was found to decrease with increasing Se content. The highest σ of 1.6 × 10⁵ S m⁻¹ at room temperature was reached at x = 0.12 with a growth rate of 0.8 mm h⁻¹. The Seebeck coefficient, S, was less dependent on Se content, all with positive values showing p-type characteristics, and the highest S was measured to be 240 μV K⁻¹ at x = 0.24. The lowest thermal conductivity, κ, was 0.7 W m⁻¹ K⁻¹ at x = 0.36. The electronic part of κ, κ_el, showed a decrease with increasing Se content, which implies that the hole concentration as the main carriers was reduced by the addition of Se. The highest dimensionless figure of merit, ZT, at room temperature was 1.2 at x = 0.36, which is attributed to the combination of a rather high electrical conductivity and Seebeck coefficient and low thermal conductivity.     

In situ synthesis and characterization of polyaniline–CaCu3Ti4O12 nanocrystal composites

High dielectric constant (ca. 2.4 × 10⁶ at 1 kHz) nanocomposite of polyaniline (PANI)/CaCu₃Ti₄O₁₂ (CCTO) was synthesized using a simple procedure involving in situ polymerization of aniline in dil. HCl. The PANI and the composite were subjected to X-ray diffraction, Fourier transform infrared, thermo gravimetric, scanning electron microscopy and transmission electron microscopy analyses. The presence of the nanocrystallites of CCTO embedded in the nanofibers of PANI matrix was established by TEM. Frequency dependent characteristics of the dielectric constant, dielectric loss and AC conductivity were studied for the PANI and the composites. The dielectric constant increased as the CCTO content increased in PANI but decreased with increasing frequency (100 Hz–1 MHz) of measurement. The dielectric loss was two times less than the value obtained for pure PANI around 100 Hz. The AC conductivity increased slightly up to 2 kHz as the CCTO content increased in the PANI which was attributed to the polarization of the charge carriers.     

Electrochemical performance of magnetron sputter deposited LiFePO4-Ag composite thin film cathodes

LiFePO₄ thin films have been sputtered from a pure LiFePO₄ target onto Ag/SS, Ag/Si₃N₄/Si and Si₃N₄/Si substrates. All of the deposited films were annealed at 973 K for 1 hr in H₂/Ar (5 %) atmosphere. Substrate induced microstructural and crystallographic evolutions have been observed by a scanning electron microscope and X-ray diffraction. Energy dispersion spectra and X-ray photoelectron spectra revealed that Ag was mixed in the LiFePO₄ films deposited on Ag under layers. Ceramic metal composite thin films were obtained. The film conductivity (1 × 10^− 3 Scm^− 1) is therefore elevated by an order of six, compared with pure LiFePO₄ (10^− 9 Scm^− 1). The electrochemical measurements of the LiFePO₄-Ag films showed a flat plateau at 3.4 V (v.s. Li/Li⁺) and a reversible capacity of 80 mAh/g. Optimization of Ag contents may further improve the discharge capacity.     

Infrared spectroscopic properties of Tm, Ho:NaY(WO4)2 single crystals

Singly doped and Tm³⁺/Ho³⁺ co-doped NaY(WO₄)₂ single crystals were grown successfully by Czochralski method. The room temperature polarized absorption and fluorescence spectra as well as the decay curves were measured. Spectroscopic parameters related to the laser operation around 2.0 μm via the ³F₄ → ³H₆ (Tm³⁺) and ⁵I₇ → ⁵I₈ (Ho³⁺) transitions have been evaluated. The energy level scheme and energy transfer processes of Tm³⁺ and Ho³⁺ were analyzed.     

Polarized spectral analysis of Er ions in Er:LiGd(MoO4)2 crystal

The Er³⁺:LiGd(MoO₄)₂ crystal with Ø21 × 33 mm³ was grown by the Czochralski technique, and the absorption spectra, the fluorescence spectra and the fluorescence decay curves were measured at room temperature. Some spectroscopic parameters, such as the parameters of oscillator strengths, the spontaneous transition probabilities, the fluorescence branching ratios, the radiative lifetimes and the emission cross-sections were estimated based on Judd-Ofelt theory and Füchtbauer-Ladenburg method. The infrared emission at 1450-1650 nm, due to ⁴I_13/2 → ⁴I_15/2 transition and the visible emission at 520-569 nm corresponding to ²H_11/2,⁴S_3/2 → ⁴I_15/2 transition were observed in Er³⁺:LiGd(MoO₄)₂ crystals under 979 nm excitation at room temperature. The emission cross-sections are 4.37 × 10⁻²⁰ cm² at 553 nm and 0.584 × 10⁻²⁰ cm² at 1561 nm for π-polarization, and the following measured lifetimes are 4.57 ms and 10.74 μs. The upconversion emissions were attributed to energy transfer between Er³⁺ ions and the excited state absorption.     

Preparation, structure and photoluminescence of nanoscaled-Nd: Lu3Al5O12

Nd:Lu₃Al₅O₁₂ (Nd:LuAG) nano-crystalline was synthesized by co-precipitation method. Its phase transformation, structure, absorption and photoluminescence properties were studied. The Nd:LuAG polycrystalline phase is formed above 900 °C and its particle sizes are in the range of 18-36 nm. The structure of Nd:LuAG was refined by Rietveld method. The lattice parameters and the distortion of Lu³⁺-O²⁻ polyhedron in Nd:LuAG are larger than that of in pure LuAG. Because the distortion of Lu³⁺-O²⁻ polyhedron is larger than that of Y³⁺-O²⁻ polyhedron in YAG and the distance of Lu³⁺-O²⁻ is smaller than that of Y³⁺-O²⁻ in YAG, Nd³⁺ in LuAG experiences a stronger crystal field effect, which is proved by the crystal field strength and the chemical environment parameter. The absorption spectrum shows that Nd:LuAG has a broad absorption band at 808 nm with FWHM above 6 nm, which is favorable for improving laser efficiency. The fluorescence lifetime from ⁴F_3/2 → ⁴I_11/2 transition is 320 μs and longer than that of Nd:YAG. The longer lifetime is propitious to energy storage. The emission cross section at 1064 nm is 2.89 × 10⁻¹⁹ cm², taking into account the Boltzmann distribution of the excited state. The emission cross section in Nd:LuAG is also larger than that of Nd:YAG, which is useful for laser operation. All results indicate that Nd:LuAG is a promising crystal material to apply in high energy lasers.     

Low temperature synthesis of Fe3O4 micro-spheres and its application in lithium ion battery

Fe₃O₄ micro-spheres with nanoparticles close-packed architectures were synthesized via a simple chemical method using (NH₄)₂Fe(SO₄)₂·6H₂O, hexamethylenetetramine, and NaF as reaction materials. This chemical synthesis took place in a vitreous jar under low temperature (90 °C) and atmospheric pressure. The morphology and structure of the as-synthesized products were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Raman spectrum. Electrochemical properties of the as-synthesized Fe₃O₄ micro-spheres as anode electrode of lithium ion batteries were studied by conventional charge/discharge tests, which exhibit steady charge/discharge platforms at different current densities. The as-prepared Fe₃O₄ electrode shows high initial discharge capacity of 1166 and 1082 mAh g⁻¹ at current density of 0.05 and 0.1 mA cm⁻², respectively.     

Structural, optical and electrical properties of CuIn5S8 thin films grown by thermal evaporation method

Stoichiometric compound of copper indium sulfur (CuIn₅S₈) was synthesized by direct reaction of high purity elemental copper, indium and sulfur in an evacuated quartz tube. The phase structure of the synthesized material revealed the cubic spinel structure. The lattice parameter (a) of single crystals was calculated to be 10.667 Å. Thin films of CuIn₅S₈ were deposited onto glass substrates under the pressure of 10⁻⁶ Torr using thermal evaporation technique. CuIn₅S₈ thin films were then thermally annealed in air from 100 to 300 °C for 2 h. The effects of thermal annealing on their physico-chemical properties were investigated using X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM), optical transmission and hot probe method. XRD studies of CuIn₅S₈ thin films showed that as-deposited films were amorphous in nature and transformed into polycrystalline spinel structure with strong preferred orientation along the (3 1 1) plane after the annealing at 200 °C. The composition is greatly affected by thermal treatment. From the optical transmission and reflection, an important absorption coefficient exceeds 10⁴ cm⁻¹ was found. As increasing the annealing temperature, the optical energy band gap decreases from 1.83 eV for the as-deposited films to 1.43 eV for the annealed films at 300 °C. It was found that CuIn₅S₈ thin film is an n-type semiconductor at 300 °C.     

Studies on the power factor of (Ba,Sr)Co2+xRu4−xO11 compounds

We have prepared polycrystalline single-phase ACo_2+xRu_4−xO₁₁ (A = Sr, Ba; 0 ≤ x ≤ 0.5) using the ceramic method and we have studied their structure, electrical resistivity and Seebeck coefficient, in order to estimate their power factor (P.F.). These layered compounds show values of electrical resistivity of the order of 10⁻⁵ Ωm and their Seebeck coefficients are positive and range from 1 μV K⁻¹ (T = 100 K) to 20 μV K⁻¹ (T = 450 K). The maximum power factor at room temperature is displayed by BaCo₂Ru₄O₁₁ (P.F.: 0.20 μW K⁻² cm⁻¹), value that is comparable to that shown by compounds such as SrRuO₃ and Sr₆Co₅O₁₅.     

Preparation, structure and electrical conductivity of the pyrochlore-type phase Sm2Zr2O7 codoped with bivalent magnesium and trivalent dysprosium cations

The pyrochlore-type phases with the compositions of SmDy_1−xMg_xZr₂O_7−x/2 (0 ≤ x ≤ 0.20) have been prepared by pressureless-sintering method for the first time as possible solid electrolytes. The structure and electrical conductivity of SmDy_1−xMg_xZr₂O_7−x/2 ceramics have been studied by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance spectroscopy measurements. SmDy_1−xMg_xZr₂O_7−x/2 (x = 0, 0.05, 0.10) ceramics exhibit a single phase of pyrochlore-type structure, and SmDy_1−xMg_xZr₂O_7−x/2 (x = 0.15, 0.20) ceramics consist of pyrochlore phase and a small amount of the second phase magnesia. The total conductivity of SmDy_1−xMg_xZr₂O_7−x/2 ceramics obeys the Arrhenius relation, and the total conductivity of each composition increases with increasing temperature from 673 to 1173 K. SmDy_1−xMg_xZr₂O_7−x/2 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10⁻⁴ to 1.0 atm at all test temperature levels. The highest total conductivity value is about 8 × 10⁻³ S cm⁻¹ at 1173 K for SmDy_1−xMg_xZr₂O_7−x/2 ceramics.     

GdBaCo2O5+δ-Sm0.2Ce0.8O1.9 composite cathodes for intermediate temperature SOFCs

The GdBaCo₂O_5+δ-Sm_0.2Ce_0.8O_1.9 (GBCO-SDC) composite cathodes were prepared, their thermogravimetric measurement, thermal expansion coefficient (TEC), electrical conductivity and electrochemical performance were studied as function of temperature and SDC content. The adjustment of TEC to electrolyte, which is one of the main problems of GBCO cathode, could be achieved to lower TEC values with more SDC addition, while maintaining reasonable high electrical conductivity. By means of DC polarization and AC impedance spectroscopy, the electrochemical performance of GBCO-SDC composite cathodes on SDC electrolyte was examined. Results indicated that the proper addition of SDC could improve the performance of GBCO cathode. The optimum content of SDC in the composite cathodes was 40 wt.% with the polarization resistance (Rp) of 1.39 Ω cm² at 500 °C, which was significantly lower than that of pure GBCO cathode (7.26 Ω cm²).     

Organoheterobimetallic cyanodithioimidocarbonates and their I2-doped products: Synthesis,characterization and conducting properties

Complexes of the type [PhHg]₂[M(cdc)₂], [Me₂Sn][M(cdc)₂], [n-Bu₂Sn][M(cdc)₂], [n-Bu₃Sn]₂[M(cdc)₂] and [Ph₃Sn]₂[M(cdc)₂] (M = Ni(II) and Cu(II); cdc²⁻ = cyanodithioimidocarbonate) and their I₂-doped products have been prepared and characterized by microanalysis, magnetic and solution as well as solid phase conductivity measurements, IR, Raman, electronic, ¹H and ¹³C NMR and ESR spectroscopic techniques. ESR silent diamagnetic compounds [PhHg]₂[Cu(cdc)₂], [Me₂Sn][Cu(cdc)₂], [n-Bu₂Sn][Cu(cdc)₂], [n-Bu₃Sn]₂[Cu(cdc)₂] and [Ph₃Sn]₂[Cu(cdc)₂] are strongly antiferromagnetically coupled. [PhHg]₂[Ni(cdc)₂] is weakly paramagnetic because of the weak axial interactions of sulfur atoms of the ligand cdc²⁻ with some of the Ni(II) centers. Sharp ¹H NMR signals suggest that [PhHg]₂[Cu(cdc)₂], [n-Bu₂Sn][Cu(cdc)₂], [n-Bu₃Sn]₂[Cu(cdc)₂] and [Ph₃Sn]₂[Cu(cdc)₂] remained diamagnetic in solution as well. Majority of the complexes exhibited σ_rt in the range of 10⁻¹¹ to 10⁻¹⁰ S cm⁻¹ while the I₂-doped products show enhanced conductivity in the 10⁻¹⁰ to 10⁻⁶ S cm⁻¹ range and exhibit semiconducting behaviour.     

Thermal conductivity of titanium dioxide films grown by metal-organic chemical vapor deposition

We studied the effect of the microstructures on the thermal conductivity of the titanium dioxide (TiO₂) films. TiO₂ films were grown by MOCVD, their morphologies were observed using a scanning electron microscope (SEM). The chemical composition was determined through Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA) measurements. The thermal conductivity of the in-plane direction was measured using an alternating current calorimetric method (laser-heating Angstrom method) in the temperature range of 300 to 470 K. The authors fabricated a TiO₂ film with extremely low thermal conductivity (~ 0.5 Wm^− 1 K^− 1), in which a feather-like texture is regularly arranged in the direction perpendicular to the heat flow. The origins of the extremely low thermal conductivity were studied from a microstructural viewpoint.     

Growth and characterization of chemical bath deposited Cd1−xZnxS thin films

Cd_1−xZn_xS (0 ≤ x ≤ 1) thin films have been deposited by chemical bath deposition method on glass substrates from aqueous solution containing cadmium acetate, zinc acetate and thiourea at 80 ± 5 °C and after annealed at 350 °C. The structural, morphological, compositional and optical properties of the deposited Cd_1−xZn_xS thin films have been studied by X-ray diffractometer, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), photoluminescence (PL) and UV-vis spectrophotometer, respectively. X-ray diffraction analysis shows that for x < 0.8, the crystal structure of Cd_1−xZn_xS thin films was hexagonal structure. For x > 0.6, however, the Cd_1−xZn_xS films were grown with cubic structure. Annealing the samples at 350 °C in air for 45 min resulted in increase in intensity as well as a shift towards lower scattering angles. The parameters such as crystallite size, strain, dislocation density and texture coefficient are calculated from X-ray diffraction studies. SEM studies reveal the formation of Cd_1−xZn_xS films with uniformly distributed grains over the entire surface of the substrate. The EDX analysis shows the content of atomic percentage. Optical method was used to determine the band gap of the films. The photoluminescence spectra of films have been studied and the results are discussed.     

Preparation and luminescent characteristics of Sr3RE2(BO3)4:Dy (RE = Y, La, Gd) phosphors for white LED

Dysprosium-activated Sr₃RE₂(BO₃)₄ (RE = Y, La, Gd) phosphors were synthesized by a high temperature solid-state reaction method. The phase uniformity of the phosphors was characterized by X-ray powder diffraction (XRD) and the luminescence characteristics were investigated. The excitation spectra at 575 nm emission show strong spectral bands in the region of 300-500 nm. The emission spectra of the phosphors with 365 nm excitation show three bands centered at 484 nm, 575 nm and 680 nm, which originate from the transitions of ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_11/2 of Dy³⁺, respectively. The effect of Dy³⁺ concentration on the emission intensity of the phosphors was investigated. The fluorescence decay curves for ⁴F_9/2 → ⁶H_13/2 excited at 365 nm and monitored at λ_em of 575 nm were measured. The decay times decreased slowly with increasing Dy³⁺ doping concentration due to a trap capturing to resonance fluorescence transfer of the activated ions and due to the exchange interactions between activated ion pairs. In order to determine the type of interaction between activated ions, the concentration dependence curves (lg(I/x) versus lg x) of Sr₃RE₂(BO₃)₄:Dy³⁺ (RE = Y, La, Gd) were plotted. The concentration quenching mechanism of the ⁴F_9/2 → ⁶H_13/2 (575 nm) transition of Dy³⁺ is the d-d interaction. All results indicate these phosphors are promising white-color luminescent materials.     

Thermoelectric properties of Cu1−xPtxFeO2 (0.0 ≤ x ≤ 0.05) delafossite-type transition oxide

The samples of Cu_1−xPt_xFeO₂ (0 ≤ x ≤ 0.05) delafossite were synthesized by solid state reaction method for studying thermoelectric properties. The properties of Seebeck coefficient, electrical conductivity and thermal conductivity were measured in the high temperature ranging from 300 to 960 K. The results of Seebeck coefficient, electrical conductivity and power factor were increased with increasing Pt substitution and temperature. The thermal conductivity was decreased from 5.8 to 3.5 W/mK with increasing the temperature from 300 to 960 K. An important results, the highest value of power factor and ZT is 2.0 × 10⁻⁴ W/mK² and 0.05, respectively, for x = 0.05 at 960 K.     

White light emission in Tm/Er/Yb tri-doped Y2O3 transparent ceramic

Tm³⁺/Er³⁺/Yb³⁺ triply doped Y₂O₃ transparent ceramics were fabricated by solid state reaction and characterized from the point of view of white light upconversion luminescence. All the samples exhibited high transparency not only in near-infrared band but also in visible region. Strong red (Er³⁺: ⁴F_9/2 → ⁴I_15/2), green (Er³⁺: ²H_11/2, ⁴S_3/2 → ⁴I_15/2) and blue (Tm³⁺: ¹G₄ → ³H₆) upconversion emissions have been observed under 980 nm excitation at room temperature. By varying the concentration of Er³⁺ ion, various colors of upconversion luminescence (pure blue, bluish green, pure green and yellowish green), including white light with CIE-X = 0.295 and CIE-Y = 0.312, can be easily achieved.