Photoelectric characteristics of nanostructured hydrochemically deposited films of the Pb<Subscript>0.975</Subscript>Sn<Subscript>0.025</Subscript>Se substitutional solid solution

The photoelectric characteristics of Pb_0.975Sn_0.025Se solid solution films prepared by the hydrochemical codeposition of PbSe and SnSe with the subsequent heat treatment in air at 573–700 K have been investigated. The thermal and optical band gaps, the temperature coefficient of the optical band gap, the dark resistance, the volt-watt sensitivity, and the range of spectral sensitivity have been determined in the temperature range of 220–300 K. It has been found that, after heat treatment below 573 K, the films of the Pb_0.975Sn_0.025Se solid solutions possess metallic conductivity, while being heat treated at elevated temperatures, they become semiconductors with p-type conductivity. The composition of the solid solution is independent of the heat treatment temperature; it is formed during deposition.     

Solid polymeric electrolyte of PVC–ENR–LiClO<Subscript>4</Subscript>

The ionic conductivity of PVC–ENR–LiClO₄ (PVC, polyvinyl chloride; ENR, epoxidized natural rubber) as a function of LiClO₄ concentration, ENR concentration, temperature, and radiation dose of electron beam cross-linking has been studied. The electrolyte samples were prepared by solution casting technique. Their ionic conductivities were measured using the impedance spectroscopy technique. It was observed that the relationship between the concentration of salt, as well as temperature, and conductivity were linear. The electrolyte conductivity increases with ENR concentration. This relationship was discussed using the number of charge carrier theory. The conductivity–temperature behaviour of the electrolyte is Arrhenian. The conductivity also varies with the radiation dose of the electron beam cross-linking. The highest room temperature conductivity of the electrolyte of 8.5 × 10⁻⁷ S/cm was obtained at 30% by weight of LiClO₄. The activation energy, E _a and pre-exponential factor, σ _o, are 1.4 × 10⁻² eV and 1.5 × 10⁻¹¹ S/cm, respectively.     

Determination of the optimal parameters for the fabrication of ZnO thin films prepared by spray pyrolysis method

In this work, ZnO thin films have been prepared by spray pyrolysis deposition method on the glass substrates. The effect of deposition parameters, such as deposition rate, substrate temperature and solution volume has been studied by X-ray diffraction (XRD) method, UV–Vis–NIR spectroscopy, scanning electron microscopy (SEM), and electrical measurements. The XRD patterns indicate polycrystalline wurtzite structure with preferred direction along (0 0 2) planes. Thin films have transparency around 90% in the visible range. The optical band gap was determined at 3.27 eV which did not change significantly. Evolution of electrical results containing the carriers’ density, sheet resistance and resistivity are in agreement with structural results. All the results suggest the best deposition parameters are: deposition rate, R = 3 ml/min, substrate temperature, T _s = 450°C and thickness of the thin films t = 110–130 nm.     

Luminescence of CaGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>:Eu crystals

We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa₂Se₄:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm is due to intracenter transitions 4f⁶ 5d–4f⁷ (⁸S_7/2) of the Eu²⁺ ions. From the temperature dependence of the intensity (log I–10³/T), we determined the activation energy (E _a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths: 0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu²⁺ ions in the CaGa₂Se₄ crystal found from the luminescence decay kinetics is 3.8 μsec. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009.     

Impedance spectroscopy study of Pb<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript> compound

The lead pyrophosphate, Pb₂P₂O₇, compound was prepared by conventional solid-state reaction and identified by X-ray powder diffractometer. Pb₂P₂O₇ has a triclinic structure whose electrical properties were studied using impedance spectroscopy technique. Both impedance and modulus analysis exhibit the grain and grain boundary contribution to the electrical response of the sample. The temperature dependence of the bulk and grain boundary conductivity were found to obey the Arrhenius law with activation energies E _g = 0.66 eV and E _gb = 0.67 eV, respectively. The scaling behavior of the imaginary part of the complex impedance suggests that the relaxation describes the same mechanism at various temperatures.     

Investigation on structural characteristics of PVDF–AgCF<Subscript>3</Subscript>SO<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite solid polymer electrolyte system

There has been an increasing interest towards the incorporation of nanosize ceramic fillers in polymer electrolytes. Solid polymer electrolytes based on polyvinylidene fluoride (PVDF), silver triflate (AgCF₃SO₃), and x wt% of aluminum oxide (Al₂O₃) nanopowders (where x = 1, 3, 5, and 10, respectively) have been prepared using solution casting technique. The structural characteristics of these thin film specimens were studied using Fourier transform infrared (FTIR) and X-ray diffraction (XRD) patterns at room temperature. The appearance of new absorption bands and gradual shifts observed in some characteristic peaks confirmed the complex formation between polyvinylidene fluoride and silver triflate. Furthermore, the addition of nanosized filler Al₂O₃ has also indicated the interaction of the filler with the polymer salt complex. The XRD patterns obtained for all these samples in the 2θ range 10° to 70° showed the amorphous nature of these samples. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9, 2006.     

Structural investigation on PEO-based polymer electrolytes dispersed with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

Thin solid polymer electrolytes based on polyethylene oxide (PEO) and silver triflate (AgCF₃SO₃) dispersed with various concentrations of aluminum oxide (Al₂O₃) nanoparticles have been prepared by solution casting technique. These thin polymer films are found to have thickness of the order of 30 to 100 μm. The X-ray diffraction (XRD) patterns have indicated the amorphous nature of the polymer electrolyte. The differential scanning calorimeter (DSC) traces showed slight change in the glass transition temperature (T _g) whereas the degree of crystallization (X _c) decreases markedly due to the addition of alumina nanoparticles. Fourier transform infrared (FTIR) spectral analysis of all these samples has revealed the presence of absorption bands around 1,000 cm⁻¹; thus indicating the complexation of silver ions with oxygen in PEO. Employing the Wagner’s polarization technique as the standard method, the total ionic transference number for the complexed polymer electrolyte was found to be approximately unity thereby revealing that the significant contribution to electrical conduction was due to ions only. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9, 2006     

Pseudo-capacitive properties of LiCoO<Subscript>2</Subscript>/AC electrochemical capacitor in various aqueous electrolytes

LiCoO₂ particles were synthesized by a sol-gel process. X-ray diffraction analysis reveals that the prepared sample is a single phase with layered structure. A hybrid electrochemical capacitor was fabricated with LiCoO₂ as a positive electrode and activated carbon (AC) as a negative electrode in various aqueous electrolytes. Pseudo-capacitive properties of the LiCoO₂/AC electrochemical capacitor were determined by cyclic voltammetry, charge–discharge test, and electrochemical impedance measurement. The charge storage mechanism of the LiCoO₂-positive electrode in aqueous electrolyte was discussed, too. The results showed that the potential range, scan rate, species of aqueous electrolyte, and current density had great effect on capacitive properties of the hybrid capacitor. In the potential range of 0–1.4 V, it delivered a discharge specific capacitance of 45.9 Fg^–1 (based on the active mass of the two electrodes) at a current density of 100 mAg^–1 in 1 molL^–1 Li₂SO₄ aqueous electrolyte. The specific capacitance remained 41.7 Fg^–1 after 600 cycles.     

氢气引入对宽光谱Mg和Ga共掺杂ZnO透明导电薄膜的特性影响

为适应宽光谱高效率硅基薄膜太阳电池的应用需求,本文尝试采用直流磁控溅射技术在553 K衬底温度下生长氢化Mg和Ga共掺杂ZnO(HMGZO)透明导电氧化物(TCO)薄膜.通过对薄膜微观结构、表面形貌、电学以及光学性能的测试和分析,详细地研究了氢气(H2)流量(0—16.0 sccm)对HMGZO薄膜结晶特性及光电性能的影响.实验结果表明:生长获得的HMGZO薄膜均为六角纤锌矿结构的多晶薄膜,择优取向为(002)晶面生长方向.薄膜的生长速率随着氢气流量的增加呈现逐渐减小趋势,主要归因于溅射产额的减小.适当的氢气引入会引起晶粒尺寸的增加.随着氢气流量由0增加至4.0 sccm,ZnO薄膜电阻率从177?·cm急剧减小至7.2×10-3?·cm,主要是由于H施主的引入显著地增加了载流子浓度;然而进一步增加氢气流量(4.0—16.0 sccm)造成电阻率的轻微增加,主要归因于载流子浓度的减小以及过多氢杂质引入造成杂质散射的增加.所有生长获得的HMGZO薄膜平均光学透过率在波长λ～320—1100 nm范围内可达87%以上.由于Mg的作用及Burstein-Moss效应的影响造成了带隙展宽,带隙变化范围～3.49—3.70 eV,其中最大光学带隙Eg可达～3.70 eV.     

Photoluminescence of CuInS<Subscript>2</Subscript> single crystals grown by traveling heater and chemical vapor transport methods

Photoluminescence of CuInS₂ single crystals grown by both the traveling heater method (THM) and chemical vapor transport (CVT) has been investigated at 4.2, 78, and 300 K. Intense emission in the near-band-edge region caused by free and bound excitons has been detected for both types of crystals. Taking into account the energy position of the luminescence line of the ground (n = 1) and first excited (n = 2) states, the binding energy for free A excitons has been estimated to be about 19.7 and 18.5 meV for CuInS₂ grown by CVT and THM, respectively. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 232–236, March–April, 2009.     

Structural and electrical properties of pure and H<Subscript>2</Subscript>SO<Subscript>4</Subscript> doped (PVA)<Subscript>0.7</Subscript>(NaI)<Subscript>0.3</Subscript> solid polymer electrolyte

Solid polymer electrolytes (SPE) based on poly-(vinyl alcohol) (PVA)_0.7 and sodium iodide (NaI)_0.3 complexed with sulfuric acid (SA) at different concentrations were prepared using solution casting technique. The structural properties of these electrolyte films were examined by X-ray diffraction (XRD) studies. The XRD data revealed that sulfuric acid disrupt the semi-crystalline nature of (PVA)_0.7(NaI)_0.3 and convert it into an amorphous phase. The proton conductivity and impedance of the electrolyte were studied with changing sulfuric acid concentration from 0 to 5.1 mol/liter (M). The highest conductivity of (PVA)_0.7(NaI)_0.3 matrix at room temperature was 10⁻⁵ S cm⁻¹ and this increased to 10⁻³ S cm⁻¹ with doping by 5.1 M sulfuric acid. The electrical conductivity (σ) and dielectric permittivity (ε′) of the solid polymer electrolyte in frequency range (500 Hz–1 MHz) and temperature range (300–400) K were carried out. The electrolyte with the highest electrical conductivity was used in the fabrication of a sodium battery with the configuration Na/SPE/MnO₂. The fabricated cells give open circuit voltage of 3.34 V and have an internal resistance of 4.5 kΩ.     

dielectric relaxation in VDF<Subscript>60</Subscript>/Tr<Subscript>40</Subscript> and VDF<Subscript>88</Subscript>/Te<Subscript>12</Subscript> polar copolymers embedded in porous glass matrices

The dielectric properties of composite materials prepared by embedding P(VDF₆₀/Tr₄₀) and P(VDF₈₈/Te₁₂) polar copolymers in porous glass matrices with a mean flow-through pore diameter of around 320 nm were investigated in the temperature range 200–450 K. Strong dielectric relaxation, the characteristic time of which conformed to the Williams-Landel-Ferry law, was observed in the vicinity of glass transition point T _g of an amorphous fraction of polymer inclusions. An increase (≈10 K) in the T _g temperature of the amorphous fraction of incorporated polymeric materials was detected.     

Optical absorption in layered MnGaInS<Subscript>4</Subscript> single crystals

Optical absorption in MnGaInS₄ single crystals has been studied. Direct and indirect optical transitions are found to occur in the range of photon energies of 2.37–2.74 eV and in the temperature range of 83–270 K. The temperature dependence of the band gap has been determined; its temperature coefficients E _gd and E _gi are −5.06 × 10⁻⁴ and −5.35 × 10⁻⁴ eV/K, respectively. MnGaInS4 single crystals exhibit anisotropy in polarized light at the absorption edge; the nature of this anisotropy is explained.     

Dielectric and phase transition of BaTi<Subscript>0.6</Subscript>Zr<Subscript>0.4</Subscript>O<Subscript>3</Subscript> ceramics prepared by a soft chemical route

BaTi_0.6Zr_0.4O₃ (BTZ) ceramic was synthesized by a soft chemical route. X-ray diffraction at room temperature shows that the sample has cubic perovskite structure with space group Pm-3m. Temperature dependent dielectric study of the sample has been investigated in the frequency range from 50 Hz to 1 MHz. The density of the sample was determined using Archimedes’ principle and found to be ∼ 97% of the X-ray density. The average grain size in the pallet was found to be ∼ 1 μm. The dielectric constant peaks at temperature T_m which is dependent on the frequency. The dielectric relaxation rate follows the Vogel–Fulcher relation with activation energy = 0.0185 eV, and freezing temperature = 186 K. All these measurements confirm that BTZ is a relaxor ferroelectric. PACS 77.22.Jp; 77.84.-s; 77.80.Bh; 77.22.Gm     

Exciton absorption spectrum of thin CsPbI<Subscript>3</Subscript> and Cs<Subscript>4</Subscript>PbI<Subscript>6</Subscript> films

A method for preparing thin films of CsPbI₃ and Cs₄PbI₆ complex compounds has been developed. Their absorption spectrum is investigated in the energy range of 2–6 eV at temperatures from 90 to 500 K. It is found that the CsPbI₃ compound is unstable and passes to the Cs₄PbI₆ phase upon heating at T ≥ 400 K.     

Transmission spectra of films of Mn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se solid solutions

Films of Mn_1−x Fe _x Se (x = 0–0.45) solid solutions were flash-sputtered. We measured the transmission spectra of the films in the wavelength range 200–1000 nm at room temperature. From these spectra, we calculated the absorption coefficients and determined the fundamental absorption edge, the position of which is shifted from 2.65 eV in MnSe to 2.30 eV in solid solutions of compositions x = 0.20–0.45. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 136–138, January–February, 2007.     

Electrical characterization of the [N(CH<Subscript>3</Subscript>)<Subscript>4</Subscript>][N(C<Subscript>2</Subscript>H<Subscript>5</Subscript>)<Subscript>4</Subscript>]ZnCl<Subscript>4</Subscript> compound

The [N(CH₃)₄][N(C₂H₅)₄]ZnCl₄ compound has been synthesized by a solution-based chemical method. The X-ray diffraction study at room temperature revealed an orthorhombic system with P2₁2₁2 space group. The complex impedance has been investigated in the temperature and frequency ranges 420–520 K and 200 Hz–5 MHz, respectively. The grain interior and grain boundary contribution to the electrical response in the material have been identified. Dielectric data were analyzed using the complex electrical modulus M ^* for the sample at various temperature. The modulus plots can be characterized by full width at half height or in terms of a non-exponential decay function ϕ(t) = exp[(−t/τ) ^β ]. The detailed conductivity study indicated that the electrical conduction in the material is a thermally activated process. The variation of the AC conductivity with frequency at different temperatures obeys the Almond and West universal law.     

Dielectric spectroscopy study of the new compound [C<Subscript>12</Subscript>H<Subscript>17</Subscript>N<Subscript>2</Subscript>]<Subscript>2</Subscript>CdCl<Subscript>4</Subscript>

The temperature dependence of the electrical conductivity of the compound 2,4,4-trimethyl-4,5-dihydro-3H-benzo[b] [1,4] diazepin-1-ium tetrachlorocadmiate in the different phases follows the Arrhenius law. The imaginary part of the permittivity constant is analyzed with the Cole–Cole formalism. In the temperature range 348–394 K, the activation energy of conductivity obtained from complex permittivity in regions I and II are, respectively, 1.03 and 0.33 eV, and E _m (in regions I and II are, respectively, 0.97 and 0.36 eV) obtained from the modulus spectra is close, suggesting that the ion transport is probably due to a hopping mechanism. The Kohlrausch–Williams–Watts function, j(t) = exp( - ( \fractt_\textKWW )^b ) \varphi (t) = \exp \left( { - {{\left( {\frac{t}{{{\tau_{\text{KWW}}}}}} \right)}^\beta }} \right) , and the coupling model are utilized for analyzing electric modulus at various temperatures. The decreasing of β at 373 K is due to approaching the temperatures of change in the conduction mechanism of the sample.     

Luminescence and electronic excitations in KBe<Subscript>2</Subscript>BO<Subscript>3</Subscript>F<Subscript>2</Subscript> crystals

This paper reports on a study of the dynamics of electronic excitations in KBe₂BO₃F₂ (KBBF) crystals by low-temperature luminescent vacuum ultraviolet spectroscopy with nanosecond time resolution under photoexcitation by synchrotron radiation. The first data have been obtained on the kinetics of photoluminescence (PL) decay, time-resolved PL spectra, time-resolved PL excitation spectra, and reflection spectra at 7 K; the estimation has been performed for the band gap E _g = 10.6−11.0 eV; the predominantly excitonic mechanism for PL excitation at 3.88 eV has been identified; and defect luminescence bands at 3.03 and 4.30 eV have been revealed. The channels of generation and decay of electronic excitations in KBBF crystals have been discussed.     

Electrochromic materials from the visible to the infrared region: an example WO<Subscript>3</Subscript>

Herein, the example of the most typical electrochromic material, namely WO₃, is used to illustrate the potential of electrochromic materials for controlling infrared reflectance and hence, emissivity. Playing with various growth parameters, contrast in reflectance between the inserted H _xWO₃ and deinserted WO₃ states as high as 73% in mid-wavelength band (MW, 3–5 μm) was achieved for 320 nm WO₃ films. The latter electrochromic materials were radio frequency sputtered on Au substrate at ambient temperature in 6 Pa of chamber pressure. In comparison, for long wavelength band (LW, 8–12 μm), the contrast in reflectance did not exceed 30%. The origins of the various electrochromic behaviours are correlated to the film structure, morphology and composition, indicating better properties for porous, nonstoichiometric films. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.