共查询到20条相似文献,搜索用时 31 毫秒
1.
An anomalous change in the electrical conductivity near the phase transition temperature (343 K) is revealed in a PbSe + PbSeO3 two-phase polycrystalline composite. It is demonstrated that the observed effect can be used in the design of chemical gas sensors, in which the chemisorption of a reducing or oxidizing gas on the surface of the PbSe + PbSeO3 composite should lead to a significant change in the electrical conductivity at temperatures close to the phase transition point. The PbSe + PbSeO3 composite is studied by impedance spectroscopy in the temperature range 293–393 K in a dry air atmosphere. It is found that the interaction of the sample with air oxygen under the controlled joint action of an ac electric field and heat can lead to both reversible and irreversible changes in the electrical conductivity. 相似文献
2.
V. V. Tomaev 《Glass Physics and Chemistry》2009,35(6):660-667
The dependences of the permittivity and electrical resistivity on the temperature and the frequency of the clock signal in
electrochemical cells fabricated from a two-phase composite of the PbSe + PbSeO3 system in the form of pressed pellets have been investigated by impedance spectroscopy. It has been shown that the composites
under investigation in the temperature range above the phase transition temperature obey the Curie-Weiss law. The Curie constant
has been estimated and the phase transition temperature (the Curie temperature) has been determined from the temperature dependence
of the inverse permittivity. 相似文献
3.
It is difficult to research on the surface structure of amorphous phase in fly ash during leaching reaction due to crystalline phase and complex structure. In the present work, in order to reveal the effects of leaching reaction on the surface structure of amorphous phase in fly ash, the modelling CaO-Fe2O3-Al2O3-SiO2 glass was prepared by the traditional melting methods. The leaching reaction of CaO-Fe2O3-Al2O3-SiO2 glass with 7.5 M KOH was investigated by spectroscopy, spectrophotometer and wet chemical method. The results show that the content of Q 1, Q 2, Q 3 and Q 4 of glass without corrosion was 4.21, 9.51, 23.03 and 52.55%, respectively, which shows that the network polymerization of glass is compact. The leaching reaction of glass can be described by the following equation: dS/dt = k/(r + S 0). Leaching in KOH for various times induces the content of Q 4 and Q 1 to be decreased, and Q 2 and Q 3 increased, resulted in the depolymerization of network and the surface glass dissolved in alkaline solution to form a gel phase. In stage one of leaching reaction, the rate of iron ion leached from glass surface was slow, which resulted in the small slope of straight-line relationship of leaching curve. In the following stage, the leaching rate of iron ion increased with the prolongation of time. 相似文献
4.
The thermal properties of compounds of the general formula Bi m + 1 Fe m ? 3 Ti3O3m + 3, which are layered perovskite-like phases of the Aurivillius type, are investigated as a function of their composition. It is demonstrated that the temperature of decomposition of the Bi m + 1 Fe m ? 3 Ti3O3m + 3 compounds decreases with an increase in the thickness of perovskite-like layers alternating in the structure and that the composition dependence of the temperature of the structural transition observed in these compounds exhibits a more complex behavior. The linear thermal expansion coefficients of all the compounds under investigation are found to be virtually independent of the composition. 相似文献
5.
A. Elbasset S. Sayouri F. Abdi T. Lamcharfi L. Mrharrab 《Glass Physics and Chemistry》2017,43(1):91-97
Single phased Sr substituted BaTiO3 ceramics were synthesized by a sol-gel route and were found to crystallise in tetragonal symmetry with P4mm space group using rietveld refinement. With increase in Sr content the tetragonality was reduced to pseudocubic and the Curie temperature (T c) decreased with a rate of 3.33 K/mol %. This transition temperature has been determined by studying the thermal evolution of Cole- Cole diagrams (ε'' vs ε'). Effects of Sr content (x) and sintering time (4 and 8 h) on density, crystalline structure and piezoelectric properties were also investigated. 相似文献
6.
A new compound, CdPb2O2Cl2, is synthesized by the method of solid-phase reactions. The compound has monoclinic symmetry, space group C2/m, a = 12.392(8) Å, b = 3.8040(14) Å, c = 7.658(5) Å, β = 122.64(5)°, and V = 304.0(3) Å3. The structure contains one symmetrically independent position of the Pb2+ cation coordinated by three O2? anions (Pb2+-O2? = 2.29–2.34 Å) and five Cl? anions (Pb2+-Cl? = 3.35–3.57 Å). The Cd2+ cation has a symmetric coordination with the formation of two bonds Cd-O = 2.15 Å and four bonds Cd-Cl = 2.73 Å. The oxygen atom is tetrahedrally coordinated by three Pb2+ cations and one Cd2+ cation, which leads to the formation of oxo-centered heterometallic OPb3Cd tetrahedra. The tetrahedra are linked together into chains through common Pb atoms and into layered complexes due to sharing of the equatorial Cd atoms. The chlorine atoms are located above the cavities of the oxo-centered layer. 相似文献
7.
The crystal structure of Pb6O[(Si6Al2)O20)] is investigated using X-ray diffraction. The compound has tetragonal symmetry, space group I4/mmm, a = 11.7162(10) Å, c = 8.0435(12) Å, and V = 1104.13(2) Å3. The structure is refined to R 1 = 0.036 for 562 unique reflections with [F 0] ≥ 4σF. The structure contains two symmetrically independent positions of the Pb2+ cations coordinated by five O atoms (Pb2+-O2? = 2.34–2.68 Å). The TO4 tetrahedra (T = Si, Al) form tubular [(Si6Al2)O20] chains extended along the c axis. The O4 oxygen atom is not bonded to the Si and Al atoms and is octahedrally coordinated by six Pb atoms with the formation of an oxo-centered OPb6 octahedron. The assumption is made that, in some of lead silicate and aluminosilicate glasses, a number of oxygen atoms are located outside the tetrahedral structure and represent segregation centers of the Pb2+ cations due to the formation of oxo-centered complexes. 相似文献
8.
The electrical properties of the PbSe + PbSeO3 two-phase polycrystalline composite are investigated by impedance spectroscopy in the temperature range 293–393 K. The frequency dependences of the ohmic resistance and the reactance of the samples under investigation are measured at different temperatures. The results obtained are used to construct the loci of the impedance in the ohmic resistance (Z′) and reactance (Z′) coordinates of the total impedance Z. The activation energies for all individual components contributing to electrical conduction in the composite are determined by impedance spectroscopy. An equivalent electric circuit that represents the integral electric response of all individual components of the sample is proposed. 相似文献
9.
A cathode material for lithium-ion batteries–LiNi1/3Co1/3Mn1/3O2–was prepared by solution combustion synthesis and characterized by XRD, SEM, and galvanostatic charge/discharge cycling. The sample calcined at 950°C for 10 h showed best charge/discharge performance. An initial discharge capacity (C) of 150.5 mA h g–1 retained 95.7% of its value after 75 charge/discharge cycles at Ic = 14 mA g–1 (0.2C rate), Id = 70 mA g–1 (0.5C rate). 相似文献
10.
A series of well-defined novel amphiphilic temperature-responsive graft copolymers containing PCL analogues P(αClεCL-co-εCL) as the hydrophobic backbone, and the hydrophilic side-chain PEG analogues P(MEO2MA-co-OEGMA), designated as P(αClεCL-co-εCL)-g-P(MEO2MA-co-OEGMA) have been prepared via a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The composition and structure of these copolymers were characterized by 1H NMR and GPC analyses. The self-assembly behaviors of these amphiphilic graft copolymers were investigated by UV transmittance, a fluorescence probe method, dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses. The results showed that the graft copolymers exhibited the good solubility in water, and was given the low critical temperature (LCST) at 35(±1) °C, which closed to human physiological temperature. The critical micelle concentrations (CMC) of P(αClεCL-co-εCL)-g-P(MEO2MA-co-OEGMA) in aqueous solution were investigated to be 2.0 × 10?3, 9.1 × 10?4 and 1.5 × 10?3 mg·mL?1, respectively. The copolymer could self-assemble into sphere-like aggregates in aqueous solution with diverse sizes when changing the environmental temperature. The vial inversion test demonstrated that the graft copolymers could trigger the sol-gel transition which also depended on the temperature. 相似文献
11.
Layered ceramics based on bismuth–calcium cobaltite with varied cobalt oxide contents is synthesized by the solid-phase method, the ceramics phase composition is determined, and the microstructure, thermal expansion, electroconductivity, and thermal electromotive force are investigated. The formation of just one compound, ternary oxide composed of Bi2Ca2Co1.7O y , is established within the quasi-binary Bi2Ca2O5–CoO z system. The effect of the cobalt oxide content on the Bi2Ca2Co x O y ceramics’ microstructure and physicochemical properties is analyzed. The single-phased ceramic sample Bi2Ca2Co1.7O y demonstrated the highest power factor value among all the investigated samples—26.0 μW/(m K2) at a temperature of 300 K. This sample showed the lowest value of the thermal linear expansion coefficient of 9.72 × 10–6 K–1. 相似文献
12.
The density d at a temperature of 25°C is measured by the hydrostatic weighing method, the Vickers microhardness H V is determined, and the fluctuation free volume fraction f g is calculated for glasses in the SrO-B2O3-SiO2 system with a constant strontium oxide content in the range from 35 to 45 mol %. It is demonstrated that the quantities H V and f g decrease and the density d increases with an increase in the SrO content. 相似文献
13.
E. K. Yukhno L. A. Bashkirov P. P. Pershukevich S. V. Slonskaya N. A. Mironova-Ulmane A. G. Sharakovskis 《Glass Physics and Chemistry》2016,42(4):379-385
Using a solid-phase method, single-phase solid solutions of La1–x Nd x InO3 (x = 0.007, 0.02, 0.05), LaIn0.99Cr0.01O3, and La0.95Nd0.05In0.995Cr0.005O3 have been obtained and their excitation and photoluminescence (PL) spectra have been studied at room temperature. It is found that the intensity of excitation and PL bands for La1–x Nd x InO3 solid solutions depends on the degree of the substitution of La3+ ions by Nd3+ ions. A solid solution with 0.02 < x < 0.05 possesses the largest intensity of the PL bands in IR wavelength range of 850–950, 1040–1100, and 1350–1370 nm. It is found that replacing 0.5% of In3+ ions in a solid solution of La0.95Nd0.05InO3 by Cr3+ ions leads to a substantial increase in the intensity of all the PL bands by exciting with light of the wavelength of λexc = 490 nm and a decrease in the intensity of all the PL bands by an excitation with light of the wavelengths of λexc = 358, 532, and 585 nm. 相似文献
14.
M. A. Luginina D. Yu. Kovalev A. E. Sytschev 《International Journal of Self-Propagating High-Temperature Synthesis》2016,25(1):35-38
Reactive sintering of 2Ti–AlN mixtures at T = 1300°C for τ = 2 h in an argon atmosphere was used to prepare Ti2AlN containing below 1 wt % TiN and exhibiting a laminate structure typical of MAX compounds. At lower values of T and τ, the TiN content of products increased. Sintering in vacuum yielded a material containing up to 20 wt % TiN. Contrary to our expectations, mechanical activation of green blends was found to increase the TiN content of sintered materials, due to intensification of thermal dissociation of AlN and elimination of Al, which shifts equilibrium toward two-phase Ti2AlN–TiN composite. Relative density of green compacts was found to produce little or no influence on phase composition of products. 相似文献
15.
T. V. Barinova I. P. Borovinskaya V. Yu. Barinov I. D. Kovalev K. B. Podbolotov 《International Journal of Self-Propagating High-Temperature Synthesis》2017,26(2):119-123
Explored was the influence of compacting pressure (P) and green density (ρ) on the properties of Zr-doped mineral-like pyrochlore ceramics Y2(Ti1 – x Zr x )2O7 (x ≤ 0.3) prepared by SHS method. The optimal ρ values that provide minimal porosity and maximal mechanical strength of synthesized ceramics were found. An increase in ρ was found to decrease combustion temperature and increase pyrochlore lattice parameter a. Green density was also found to affect phase composition of the SHS-produced ceramics under study. 相似文献
16.
A comparative study of the oxidative destruction of the monomer face-centered cubic (FCC) lattice and various polymer [dimeric (D), orthorhombic (O), tetragonal (T), and rhombohedral (R)] phases of C60 in an atmosphere of oxygen has been performed in the temperature range of 100–500°C with the use of a flow microunit connected to a gas chromatograph. From direct measurements of the content of CO2 in the gaseous products of destruction, the temperature dependences of oxidation rates are measured for the materials under study. It has been established that, with respect to stability against oxidative destruction, different forms of C60 may be arranged as follows: the monomer FCC phase of C60 > D > O > T > R. The reasons behind this tendency are discussed. 相似文献
17.
Silicophosphate glasses of nominal composition (P2 O 5 50%-SiO2 30%-Na2O 20%) and Nd2 O 3 additive (0.5 and 2 wt%) were prepared and dielectric behavior has been studied over a temperature range (302–483 K) in the frequency range (0.5 - 3243 kHz). Frequency dependence of AC conductivity (σ ac), has been explored using the universal power law. Disparity of the frequency exponent (s) with temperature was examined in terms of diverse conduction mechanisms. The principal conduction mechanisms were found correlated to both barrier hopping (CBH) and quantum mechanical tunneling (QMT) models. Temperature dependence of σ ac (ω) showed a linear increase with different frequencies. In addition, the capacitance, loss tangent, dielectric loss and dielectric constant were calculated over variable temperature ranges and frequencies. 相似文献
18.
A novel biosensor based on electro-co-deposition of myoglobin (Mb), sodium alginate (SA), Fe3O4-graphene (Fe3O4-GR) composite on the carbon ionic liquid electrode (CILE) was fabricated using Nafion as the film forming material to improve the stability of protein immobilized on the electrode surface, and the modified electrode was abbreviated as Nafion/Mb-SA-Fe3O4-GR/CILE. FT-IR and UV–vis absorption spectra suggested that Mb could retain its native structure after being immobilized in the SA-Fe3O4-GR composite film. The electrochemical behavior of the modified electrode was studied by cyclic voltammetry, and a pair of symmetric redox peaks appeared in the cyclic voltammograms, indicating that direct electron transfer of Mb was realized on the modified electrode, which was ascribed to the good electrocatalytic capability of Fe3O4-GR composite, the good biocompatibility of SA and the synergistic effects of SA and Fe3O4-GR composite. The electrochemical parameters of the electron transfer number (n), the charge transfer coefficient (α) and the electron transfer rate constant (k s) were calculated as 0.982, 0.357 and 0.234 s?1, respectively. The modified electrode exhibited good electrocatalytic ability to the reduction of trichloroacetic acid (TCA) with wide linear range from 1.4 to 119.4 mmol/L, low detection limit as 0.174 mmol/L (3σ), good stability and reproducibility. 相似文献
19.
R. S. Bubnova J. E. Anderson M. G. Krzhizhanovskaya S. K. Filatov 《Glass Physics and Chemistry》2010,36(3):369-375
Anhydrous ammonium pentaborate NH4B5O8 has been synthesized by thermal dehydration of larderellite NH4[B5O7(OH)2] · H2O at a temperature of 290°C for 7 h. The crystal structure has been determined from the X-ray powder diffraction data: a = 7.58667(5) Å, b = 12.00354(8) Å, c = 14.71199(8) Å, R p = 6.23, R wp = 7.98, R B = 12.7, R F = 8.95, and β-KB5O8 structure type. The double interpenetrating framework is formed by pentaborate groups, each consisting of a boron-oxygen tetrahedron and four triangles, in which all oxygen atoms are bridging. The thermal behavior of the NH4B5O8 compound has been investigated using thermal X-ray diffraction. As for other pentaborates of this type, the thermal expansion of the NH4B5O8 compound is anisotropic and reaches a maximum along the a axis. The thermal expansion coefficients are as follows: α a = 39 × 10?6, α b = 6 × 10?6, α c = 20 × 10?6, and α V = 65 × 10?6 °C?1. 相似文献
20.
The geometric and topological analysis of the crystal structure of intermetallic Li26Na58Ba38 (cF488, a = 27.335 Å, V = 20 424 Å3, F-43m) is carried out using computer methods (ToposPro software package). The analysis method is based on determining the chemical composition and structure of an intermetallic cluster precursor and constructing a basic 3D network of the structure in the form of a graph whose nodes correspond to the position of their centers of gravity. Using the method of the complete decomposition of the 3D factor graph of the crystal structure into cluster substructures, we find two types of framework-forming nanoclusters, namely, K69 of the 1@16@52 composition and K26 of the 0@4@22 composition with point symmetry g =–43m. The symmetric and topological code of self-assembly of 3D structures from nanocluster precursors is reconstructed in the following form: primary chain → microlayer → microframework. Clusters Ba5, Na6(Na4), and Na2В are determined as spacers occupying voids in the 3D framework of nanoclusters K69 and K26. 相似文献