共查询到20条相似文献,搜索用时 321 毫秒
1.
A. Durán A.M. Arévalo-López M. García-Guaderrama M.P. Cruz M.A. Alario-Franco 《Journal of solid state chemistry》2010,183(8):1863-1871
Microstructural, magnetothermal and dielectric properties of YCrO3 powders prepared by combustion and solid state methods have been studied by a combination of XRD, specific heat, magnetization and permittivity measurements. The TEM and XRD characterization confirm that the combustion powders are amorphous plate-like agglomerates of nano-sized crystalline particles. A more uniform grain size along with an increase of the relative density is observed by SEM in the sintered samples prepared by combustion route with respect to those produced by solid state reaction. Similar to the material obtained through solid state synthesis, the material prepared by the combustion method also shows spin canted antiferromagnetic ordering of Cr+3 (S=3/2) at ∼140 K, which is shown by magnetization as well as λ-type anomaly in the total specific heat. Furthermore, the magnetic contribution to the total specific heat reveals spin fluctuations above TN and a spin reorientation transition at about 60 K. Both YCrO3 compounds show a diffuse phase transition at about 450 K, typical of a relaxor ferroelectric, which is characterized by a broad peak in the real part of the dielectric permittivity as a function of temperature, with the peak decreasing in magnitude and shifting to higher temperature as the frequency increases. The relaxor dipoles are due to the local non-centrosymmetric structure. Furthermore, the high loss tangent in a broad range of temperature as well as conductivity analysis indicates a hopping mechanism for the electronic conductivity as we believe it is a consequence of the outer d3-shell, which have detrimental effects on the polarization and the pooling process in the YCrO3 bulk material. The more uniform particle size and higher density material synthesized through the combustion process leads to an improvement in the dielectric Properties. 相似文献
2.
A novel method for synthesizing long afterglow silicate phosphor Sr3MgSi2O8:Eu^2+,Dy^3+using TEOS and inorganic powders as reactants was reported. Acetic acid as a catalyzer controlled the hydrolysis of TEOS by adjusting pH value of the system. The morphologies of precursor were characterized by transmission electron microscope (TEM). The structure and optical properties of the phosphor powders were systematically investigated by means of X-ray diffraction and spectrofluorometry. TEM images have reflected the core-shell structure and quasi-spherical morphology of the precursor particles. It was found that the single-phase Sr3MgSi2O8 crystalline structures were obtained at 1050 and 1250 ℃ for the samples prepared with the nano-coating method and the solid state reaction, respectively. The emission intensities of the phosphors prepared by the present method were higher than those by the conventional process. Also, the afterglow characteristic was better than that prepared by solid-state reaction in the comparable condition. 相似文献
3.
Maria Ochsenkühn-Petropoulou Rachel Argyropoulou Petros Tarantilis Nikos Deftereos Evagelos Kokkinos Klaus-Michael Ochsenkühn George Parissakis 《Mikrochimica acta》2001,136(3-4):153-158
YBa2Cu3O
7−x
(x = 0.1–0.2) compounds (YBCO) were produced by the oxalate coprecipitation and the solid state reaction methods. The powders
obtained were used for the production of YBCO superconducting coatings on Pt/Si wafers, by the electrophoretic deposition
technique. The optimum process conditions for the production of both powders and coatings were found by using a combination
of modern analytical techniques. The thermal treatment of the samples was followed by thermogravimetry (TG) and differential
scanning calorimetry (DSC). The optimization and characterization of the superconducting properties of the powders and coatings
were achieved by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), optical microscopy, magnetic susceptibility
and electrical resistivity measurements. 相似文献
4.
Lithium vanadium bronzes with composition formula LixV2O5 (0.04 ≤ × ≤ 0.92) have been prepared by solid‐state reaction at 650 °C in argon atmosphere. The obtained products were characterized by X‐ray powder diffraction and IR spectroscopy. The results reveal that four phases are present in the range from x = 0.04 to 0.92, namely α, β, β′, and γ phase. The magnetic susceptibility for the investigated bronzes was measured using the conventional Gouy's method. The values of the effective magnetic moments, as calculated from experimental data, indicate the presence of V4+ ions in all bronze samples. The electrical conductivity as a function of temperature and lithium content was measured in the temperature range from room temperature to 483 K. The electrical conductivity of the bronzes is found to be affected by lithium content. The values of the electrical conductivity increase with temperature for the prepared samples and both electronic and ionic conduction are discussed. 相似文献
5.
6.
C. K. Ghosh S. R. Popuri T. U. Mahesh K. K. Chattopadhyay 《Journal of Sol-Gel Science and Technology》2009,52(1):75-81
Nanocrystalline powders of CuAlO2 were synthesized through sol–gel method using nitrate-citrate route and also through solid state reaction method. We used
a new set of precursor materials for the synthesis of CuAlO2 through sol–gel route which were not reported in the past. A little lowering of the synthesis temperature (1,000 °C) was
observed in case of sol–gel process compared to the solid state reaction method (1,100 °C) and also at shorter time duration.
The particle size of the synthesized powders was determined through small angle X-ray scattering. It has been observed that
the particle size prepared by nitrate-citrate technique is less than the particle size prepared by the solid-state reaction
method. Chemical states of the atomic species were determined by X-ray photoelectron spectroscopy. The formation of phase
pure CuAlO2 were also confirmed by Fourier transformed infrared spectroscopy. A number of solvents were also used for finding the best
possible combinations for obtaining phase pure CuAlO2 at 1,000 °C and it was observed that only the combination of nitrate salts, citric acid and ethanol resulted phase pure CuAlO2. 相似文献
7.
V. M. Novotortsev S. F. Marenkin S. A. Varnavskii L. I. Koroleva T. A. Kupriyanova R. Szymczak L. Kilanski B. Krzymanska 《Russian Journal of Inorganic Chemistry》2008,53(1):22-29
Germanium zinc diarsenide crystals with various manganese fractions, (ZnGeMn)As2, were prepared by reacting high-purity powders of zinc diarsenide, germanium, arsenic, and manganese. The manganese solubility at temperatures near the ZnGeAs2 melting temperature was 3.5 wt % as determined by X-ray fluorescence analysis. The unit cell volume decreased with rising manganese concentration. Magnetization in fields up to 50 kOe, magnetic susceptibility, electrical resistance, and Hall constants were measured over wide temperature ranges. Manganese-doped samples had spontaneous magnetization and high Curie temperatures reaching 367 K. Their magnetic properties are characteristic of spin glasses in low magnetic fields. In higher fields, the spin state changed to spontaneous magnetization. 相似文献
8.
Summary Coordination compounds of copper(II) chloride, bromide, thiocyanate and sulphate with nicotinic acid, nicotinamide and isonicotinamide have been prepared and characterized by molecular conductance, magnetic susceptibility, electronic and i.r. spectral measurements down to 200 cm–1 in the solid state. Possible stereochemistries for these complexes in the solid state are discussed. 相似文献
9.
K. Przybylski T. Brylewski M. Bućko 《Journal of Thermal Analysis and Calorimetry》1995,45(5):1099-1108
Calcination conditions of the precursor powders, i.e. temperature, type of atmosphere and duration, were determined with a view to obtain superconducting powders with the most advantageous physico-chemical properties. Investigated were powders in the Y?Ba?Cu?O system prepared by the sol-gel method. Thermogravimetric examinations of the powders have revealed that the decomposition kinetics of BaCO3 determines the formation rate of the superconducting YBa2Cu3O7?x (‘123’) phase. It follows from the decomposition kinetics of BaCO3 that the process is the most intensive in argon, whereas in static air and oxygen it is the slowest. The phase composition analysis (XRD) and low-temperature magnetic susceptibility measurements of the calcinated powders, confirm the above mentioned changes in the decomposition kinetics. The reaction of barium carbonate can be completed if the calcination process is conducted at the temperature of 850°C for 25 h, yielding easily sinterable powders for obtaining single-phase superconducting bulk samples with advantageous functional parameters. 相似文献
10.
《Journal of solid state chemistry》1987,68(1):163-176
V1−xMnxO2−2xF2x samples (0 < x ≤ 0, 10) have been prepared by solid state reaction in sealed platinium tubes. The metal ⇄ insulator transition occurs at a quickly decreasing temperatures as MnF2 increases. The crystallographic, magnetic, transport properties, and DTA have been determined and discussed. 相似文献
11.
Visible-light-driven photocatalyst of Bi2WO6 nanoparticles prepared via amorphous complex precursor and photocatalytic properties 总被引:1,自引:0,他引:1
Shicheng Zhang 《Journal of solid state chemistry》2006,179(1):62-69
The visible-light-driven photocatalyst Bi2WO6 nanoparticles have been prepared by calcining amorphous complex precursor at a relatively low temperature of above 450 oC. The effects of calcination temperature and time on the structures and properties of Bi2WO6 nanoparticles have been investigated in detail. The photocatalytic activity of the Bi2WO6 powders were evaluated by degradation of RhB molecules in water under visible light irradiation (λ>400 nm). The results showed that the particle size and grain size of Bi2WO6 increased with the calcination temperature and time. The photocatalytic activity of the best sample was about 8.8 times higher than that of the sample prepared by traditional solid state reaction and the photo-degradations was a zero-order reaction. The best route to enhance the photocatalytic activity of Bi2WO6 was to prepare the sample at a lower temperature for a longer time, due to the samples with better crystallization and smaller particle size. 相似文献
12.
The title compound is prepared by solid state reaction of the elements (773 K, 72 h) and characterized by single crystal XRD, magnetic susceptibility, thermal and electrical conductivity, thermopower, and IR measurements. 相似文献
13.
La2Mo2O9 ceramics have been prepared from freeze-dried precursors and their properties compared to those of lantanum molybdate obtained by conventional solid state (SS) reaction. All materials have been characterized by X-ray diffraction, scanning electron microscopy and thermal analysis (TGA/DTA/DSC and dilatometry) to characterize the phase formation and phase transition. When the freeze-dried method was applied, the synthesis temperature required to obtain dense samples was much lower than that for powders obtained by SS reaction. The morphology and structure of the oxide particle are significantly dependent on the synthesis method. The grain size is smaller, whereas the density of sintered pellets is higher for the freeze-dried precursor powder when compared with the SS reaction method. Impedance spectroscopy was used to measure the electrical conductivity of La2Mo2O9 from 548 to 1123 K, in air, and to characterize the blocking effects of grain boundaries. 相似文献
14.
《Electrochemistry communications》2008,10(10):1455-1458
Meso/macroporous La1−xSrxCoO3−δ powder with the specific surface area higher than 140 m2 g−1 has been synthesized from the corresponding nitrates, using solution thermal decomposition method. These nanopowders have been used for preparation of SOFC cathodes, demonstrating lower oxygen electroreduction activation energy than that for less porous cathodes prepared from the powders synthesized using traditional solid state reaction method. To increase macroporosity of the cathodes the special pore forming agent has been added into the raw cathode paste. The very low total polarization resistance and activation energy values have been obtained for oxygen electroreduction, depending on the cathode porosity and potential applied. 相似文献
15.
Maria Ochsenkühn-Petropoulou Rachel Argyropoulou Klaus-Michael Ochsenkühn 《Mikrochimica acta》2000,135(3-4):139-146
The efficiency of the production of the high temperature superconducting powders Bi2Sr2CaCu2O8+x (BSCCO 2212) using the solid state reaction in one or two step processes under different thermal treatment was compared by
means of different modern analytical techniques. Through the same techniques the optimization of the production of the production
of Bi-2212 powder produced by the two step process, was achieved. X-ray diffraction analysis (XRD) and Raman spectroscopy
were used to characterize the products for their stoichiometry and phase-purity. The grain size of the powders was observed
by scanning electron microscopy (SEM), while their superconducting properties were tested by electrical DC-resistivity and
magnetic susceptibility measurements using a superconducting quantum interference device (SQUID). It resulted that the two
step process gives a high quality BSCCO 2212 superconducting powder with T
c = 85 K, in a shorter time and with a greater recovery rate than the one step process.
Received May 3, 1999. Revision April 27, 2000. 相似文献
16.
Zn1-xCoxMoO4 (x < 0.3) powders are prepared by solid state reaction of stoichiometric mixtures of MoO3, Co3O4, and ZnO (alumina crucible, 700 °C, 20 h and 800 °C, 10 h). 相似文献
17.
Effect of Cadmium Substitution on Structural and Magnetic Properties of Nano Sized Nickel Ferrite
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Sanjay Pralhadrao Jadhav Bhagwan Ghanshamji Toksha Kamalakar Marutirao Jadhav Narayan Dadarao Shinde 《化学物理学报(中文版)》2010,23(4):459-464
The structure and crystal phase of the nanocrystalline powders of Ni1-xCdxFe2O4 (0≤x≤0.5) mixed ferrite, synthesized by wet chemical co-precipitation method, were characterized by X-ray diffraction. Results showed that the lattice parameter increased with increasing Cd concentration. Microstructure was studied by scanning electron microscopy. TG/DTA stud-ies were carried out on co-precipitated sulphate complexes. These studies revealed the low ferritization temperature (650 oC) of the ferrite system synthesized by presently adopted route of synthesis and occurrence of simultaneous decomposition and ferritization processes.Further studies by infrared spectroscopy were also conducted. Moreover, magnetic properties of the prepared nanoparticles were studied by magnetization and a.c. susceptibility mea-surements. The response of prepared Ni1-xCdxFe2O4 mixed ferrites to magnetic field was investigated. Results show that, magnetic susceptibility, Curie temperature, and effective magnetic moment decreased as the Cd content increases. 相似文献
18.
Christoph Janiak Tobias G. Scharmann Thomas Bruniger Jana Holubov Milan Ndvorník 《无机化学与普通化学杂志》1998,624(5):769-774
The spin-crossover behavior of bis{hydro-tris(1,2,4-triazolyl)borato}iron(II) is investigated in bulk and as a magnetically diluted sample in the solid state and in solution as a function of temperature by magnetic susceptibility measurements and differential scanning calorimetry. In aqueous solution the low-spin to high-spin transition is shown in turn to decrease the longitudinal relaxation time T1 of water protons with increasing temperature. The solid-state magnetically diluted samples were prepared by cocrystallization with the isostructural zinc complex. 相似文献
19.
The compounds Ba3Re2O9 and Sr3Re2O9 were prepared by the solid state reaction of the corresponding alkaline-earth oxide with ReO3 at 750 to 900°C in sealed, evacuated, fused silica tubes. The two compounds are isostructural, having the nine-layer ABO3 structure with vacant central octahedra. The unit cell parameters are given. The magnetic susceptibility for Ba3Re2O9 indicates Curie-Weiss behavior with a Re6+ moment having localized electrons. The magnetic data for Sr3Re2O9 suggest delocalized electron behavior from its temperature-independent susceptibility. Both compounds appear to have semiconducting properties, but the strontium analog is a better conductor. Both compounds are unstable when heated in air above 400°C. They are readily decomposed by chemical oxidizing agents. 相似文献
20.
A series of tantalum(V) peroxofluoro complexes of the type Et4N{Ta(O-O)-F3(diket)} (diket = β-keto-enolate) has been prepared by the reaction of β-diketones with the new compound Et4N{Ta(O-O)F4(H2O)}. The complexes have been characterised in the solid state on the basis of their analytical and infrared spectral data. When the bidentate chelating ligand is unsymmetrical, proton and fluorine nuclear magnetic resonance spectra demonstrate that the products exist as geometrical isomers in acetonitrile solutions.The orientation of the peroxo group according to the nature of the metal-ligand bonds is discussed. 相似文献