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1.
A newly substituted series of perovskites, BixLa2−xMnMO6 with M = Ni, Co and x = 0.25, 0.50, were synthesized using a citrate sol-gel technique. The crystal structure, established from neutron diffraction, is a distorted double perovskite with partial transition metal B-site ordering. These perovskites crystallize in the centrosymmetric space group, P21/n, with structures that are similar to the x = 0 end members. All samples are prone to non-stoichiometry involving substitution of Mn onto the Ni/Co sites, in addition to varying degrees of antisite disorder. The neutron powder diffraction and magnetization measurements reveal ferromagnetism in all samples with ordering temperatures between 220 K and 280 K. The M = Co samples have lower Curie temperatures, but higher coercivities. There is a clear link between the degree of transition metal site disorder and the saturation magnetization values. Electrical measurements demonstrate the presence of mixed ionic and electronic conductivity. 相似文献
2.
La2−xBaxMo2O9−x/2 (x ≤ 0.18) have been prepared by solid state reaction method. The lattice parameter of La2−xBaxMo2O9−x/2 (x ≤ 0.18) determined by XRD data refinement shows a linear dependence on the dopant Ba content x. For the specimen with a La/Ba molar ratio of 0.18-0.2, additional reflection of secondary phase exists in the XRD pattern, so the value of solubility limit for Ba in La2Mo2O9 is defined in range of 0.18 < x < 0.2. As the replacement degree of La3+ by Ba2+ increases, the bulk conductivity of La2−xBaxMo2O9−x/2 (x ≤ 0.18) decreases initially and then increases, a minimum value at La1.9Ba0.1Mo2O8.95 exists. Hebb-Wagner studies in argon atmosphere, which use an oxide-ion blocking electrode, show that La2−xBaxMo2O9−x/2 (x ≤ 0.18) are predominantly oxide-ion conducting in the temperature ranging from 773 to 1173 K. The average thermal expansion coefficient of La1.84Ba0.16Mo2O8.92 determined by high-temperature XRD was deduced as great as 17.5 × 10−6 K−1 between 298 and 1173 K. 相似文献
3.
Effects of the partial substitution of W5+,6+ for Mo5+,6+ on the structural and physical properties of Ba2CrMoO6 have been investigated. Polycrystalline Ba2CrMo1 − xWxO6samples have been prepared by sol-gel method in a stream of 5% Ar/H2 gas at various sintering temperatures. Rietveld analysis of X-ray diffraction patterns shows a partial disorder of Mo/W and Cr on the B sites of the double perovskite, which plays a dominant role in the structural and magnetic properties of these compounds. The symmetry is cubic (Fm3?m) for all samples, and no phase transition was detected for Ba2CrMo1 − xWxO6. The Curie temperature TC has been analyzed by two methods: a linear extrapolation of M(T) to zero magnetization and the thermodynamic model. The experimental results indicate that TC decrease from 335 K (x = 0) to 285 K (x = 0.5) with increasing W substitution independently of the method used to obtain TC. A systematic decrease in saturation magnetization, Ms with increasing W substitution has been observed in this solid solution series. This decrease of magnetization arises from the disorder at the Cr and Mo/W sites. Electrical properties change as well strongly along the series. 相似文献
4.
The grain size and the density of the Zn1 − xSnxO (0 ≤ x ≤ 0.05) samples decreased with increasing SnO2 content. The addition of a small amount of SnO2 (x ≤ 0.01) to ZnO led to an increase in both the electrical conductivity and the absolute value of the Seebeck coefficient, resulting in a significant increase in the power factor. The thermoelectric power factor was maximized to a value of 1.25 × 10−3 Wm−1 K−2 at 1073 K for the Zn0.99Sn0.01O sample. 相似文献
5.
Hiroyuki Tetsuka Yue Jin Shan Keitaro Tezuka Hideo Imoto 《Materials Research Bulletin》2005,40(7):1223-1232
Polycrystalline Cd3−x−yCuxAyTeO6 (A = Li, Na) samples were prepared by solid-state reaction, and their crystal structure and electrical properties were investigated. In Cd3−xCuxTeO6 and Cd3−yAyTeO6 (A = Li, Na), the maxim solubility of x and y was 0.15 and 0.15 for A = Li, 0.05 for A = Na, respectively. For co-substituted samples Cd2.9−yCu0.1LiyTeO6 and Cd2.9−yCu0.1NayTeO6, the maxim solubility of x was the same as single substitution above-mentioned. The alkali-metal substituted samples Cd3−yAyTeO6 (A = Li, Na) showed a negative Seebeck coefficient, which indicates that the major conduction carriers are electron. On the other hand, the co-substituted samples Cd2.9−yCu0.1AyTeO6 (A = Li, Na) represented a positive Seebeck coefficient, and major conduction carriers were hole through substitution by copper ions. 相似文献
6.
A series of single phase solid-solution K4Ce2Ta10−xNbxO30 (x = 0-10) photocatalysts were synthesized by conventional high temperature solid state reaction. Their UV-vis diffuse reflectance spectra showed their absorbance edges shifted to long wavelength zone consistently with the increase of the amount of Nb for substituting Ta in these compounds, and the onsets of absorbance edges ranging from about 540 nm to 690 nm, corresponding to bandgap energy of 1.8-2.3 eV. These series of photocatalysts possess appropriate band gap (ca. 1.8-2.3 eV) and chemical level to use solar energy to decompose water into H2, and the photocatalytical activities under visible light (λ > 420 nm) demonstrated that the activities decreased correspondingly with the increase of the amount of Nb in these compounds, which is regarded as the result of the differences of their band structures. Furthermore, the photocatalytical activities and the photophysical properties of these visible light-driven photocatalysts K4Ce2Ta10−xNbxO30 (x = 0-10) were bridged by the first principle calculation based on Density Functional Theory with General Gradient Approximation and Plane-wave Pseudopotential methods. 相似文献
7.
Ba1−ySryLa4−xTbx(WO4)7 (x = 0.02-1.2, y = 0-0.4) phosphors were prepared via a solid-state reaction and their photoluminescence properties were investigated. An analysis of the decay behavior indicates that the energy migration between Tb3+ ions is conspicuous in the 5D3 → 7F4 transition due to the cross-relaxation in BaLa4(WO4)7. A partial substitution of Ba2+ by Sr2+ can not only enhance the emission intensity but also increase the solid solubility of Tb3+ in Ba1−ySryLa4−xTbx(WO4)7. The emission intensity of the 5D4 → 7FJ (J = 4, 5, 6) transitions can be enhanced by increasing Sr2+ and Tb3+ concentrations, with the optimal conditions being x = 1.2, y = 0.4 (Ba0.6Sr0.4La2.8Tb1.2(WO4)7). Under near-UV excitation at 379 nm, the CIE color coordinates of Ba1−ySryLa4−xTbx(WO4)7 vary from blue (0.212, 0.181) at x = 0.04, y = 0, to green (0.245, 0.607) at x = 1.2, y = 0.4. 相似文献
8.
In this study, bulk ceramics with general formula Bi1−ySryFe(1−y)(1−x)Sc(1−y)xTiyO3 (x = 0-0.2, y = 0.1-0.3 mol%) were prepared by traditional solid-state reaction method. As a comparison, bulk BiFeO3 (BF) was also sintered by rapid sintering method. Their structural, magnetic, dielectric properties were investigated. X-ray diffraction analysis indicated that apart from a small amount of secondary phase detected in BF, all other samples crystallized in pure perovskite structure and maintained original R3c space group. The room temperature M-H curves were obtained. While BF had a coercive magnetic field (Hc) of 150 Oe, Bi1−ySryFe1−yTiyO3 solid solutions had a much larger value (for y = 0.1, 0.2, 0.3, Hc were 4537, 5230 and 3578 Oe, respectively). Sc3+ substitution decreased the Hc values of these solid solutions remarkably, and resulted in soft magnetic properties, as well as a decrease of the dielectric loss. At 1 MHz, the tan δ of Bi0.7Sr0.3Fe0.7(1−x)Sc0.7xTi0.3O3 with x = 0.05, 0.1, 0.15, 0.2 were 0.1545, 0.1078, 0.1046 and 0.1701, respectively. 相似文献
9.
Li2.6Co0.4 - xCuxN (x = 0, 0.15) anode materials were prepared by conventional solid state reaction. Between both materials, Li2.6Co0.25Cu0.15N exhibited better capacity retention than that of Li2.6Co0.4N. According to electrochemical impedance spectroscopy, the better cycling behavior of Li2.6Co0.25Cu0.15N has been attributed to the improvement in interfacial compatibility between the electrode and electrolyte interface. A possible explanation to this was given. Li2.6Co0.4 - xCuxN/Cu0.04V2O5 full-cells were assembled to investigate the reliability of Li2.6Co0.4 - xCuxN anode materials in practical applications. The Li2.6Co0.25Cu0.15N/Cu0.04V2O5 cell delivered a specific capacity of 260 mA h g− 1, and a specific energy of 505.7 mW h g− 1, which was much higher than that of C/LiCoO2 lithium ion batteries. 相似文献
10.
This paper presents the results of a study concerning the structural and electrical properties of MgAl2-2xZrxMxO4 (x = 0.00-0.20 and M = Co2+ and Ni2+) prepared by a coprecipitation technique using urea as a precipitating agent. The X-ray diffraction data for the pure and its doped samples are consistent with the single-phase spinel and their crystallite sizes are in the range 7-20 ± 4 nm. The DC resistivity increases from 3.09 × 109 Ω cm to 6.73 × 109 and 8.06 × 109 Ω cm whereas dielectric constant decreases from 5.80 to 5.11 and 4.95 on doping with Zr-Co and Zr-Ni, respectively. The electrical resistivity variations with increase in the dopant contents indicate two types of conduction mechanisms in operation. Several parameters such as, hopping energy (W), metal-semiconductor transition temperature (TMS) and Debye temperature (θD) have also been determined. The increase in DC resistivity and decrease in dielectric constant suggest that the synthesized materials can be considered for application as an insulating and structural material in fusion reactors. 相似文献
11.
Hong Lv Bin-Yuan Zhao Yu-Ji Wu Gang Sun Gang Chen Ke-Ao Hu 《Materials Research Bulletin》2007,42(12):1999-2012
The crystal structure, thermal expansion rate, electrical conductivity and electrochemical performance of Sm0.5Sr0.5MxCo1−xO3−δ (M = Fe, Mn) have been investigated. Two crystal structures have been observed in the specimens of Sm0.5Sr0.5FexCo1−xO3−δ (SSFC) at room temperature, the perovskite structure of SSFC has an orthorhombic symmetry for 0 ≤ x ≤ 0.4 and a cubic symmetry for 0.5 ≤ x ≤ 0.9. The specimens of Sm0.5Sr0.5MnxCo1−xO3−δ (SSMC) crystallize in an orthorhombic structure. The adjustment of thermal expansion rate to electrolyte, which is one of the main problems of SSC, can be achieved to lower TEC values with more Fe and Mn substitution. Especially, Sm0.5Sr0.5Mn0.8Co0.2O3−δ exhibits good thermal compatibility with La0.8Sr0.2Ga0.8Mg0.2O3. High electrical conductivities are obtained for all the specimens and they demonstrate above 100 S/cm at 800 °C in SSFC system. The polarization resistance increases with increasing Mn content, Nevertheless, the polarization resistance of SSFC increases with increasing Fe content, but when the amount of Fe reaches to 0.4, the maximum is obtained while the resistance will decrease when the amount of Fe reaches above 0.4. Sm0.5Sr0.5Fe0.8Co0.2O3−δ electrode exhibits high catalytic activity for oxygen reduction operating at temperature from 700 to 800 °C. 相似文献
12.
All-solid-state cells of the configuration (−)Ag + SE//SE//I2-phenothiazine + C(+) using the best conducting compositions of the solid electrolyte systems, namely, Cu1−xAgxI-Ag2O-Y where x = 0.05, 0.1, 0.15, 0.2 and 0.25, Y = MoO3, B2O3, SeO2, V2O5 and CrO3, as the electrolytes were fabricated. Discharge, polarization and power characteristics of these cells were also evaluated. The open circuit voltage values of these cells were in the range 620-635 mV. The stability of these cells has been indicated by the constancy of their OCV over a period of 6 months. The polarization and discharge studies on these cells have shown that typical cells based on the electrolytes with Y = B2O3, SeO2 and V2O5 would possess discharge capacities of 12.84, 3.76 and 5.05 mA h and specific energy of 6.55, 1.81 and 2.77 W h kg−1, respectively. The solid electrolytes have good electrochemical stability and compatibility with the Ag/Phenothiazine-I2 electrode couple thus offering their suitability of application in microwatt power sources. 相似文献
13.
We synthesized the spinel-type compounds belonging to the Mn2−xV1+xO4 series with x = 0, 1/3 and 1 as polycrystalline powders. Crystal and magnetic structures were refined using synchrotron X-ray and neutron powder diffraction. At 300 K all members crystallize in the cubic system, space group , and show a structural transition at low temperature, changing to a tetragonal symmetry (space group I41/amd). Cations distributions between octahedral and tetrahedral sites were refined from neutrons diffraction (ND) data and explained based on crystal field stabilization energies (CFSE) and ionic radii. The magnetic unit cell is the same as the crystallographic one, having identical symmetry relations. The magnetic structure was refined as an arrangement of collinear spins, antiferromagnetically ordered, parallel to the c-axis of the unit cell. The refined site magnetic moments are smaller than those obtained from hysteresis cycles of the M vs. H measurements, indicating that some non-collinear disordered component coexists with the ordered component along the c-axis. 相似文献
14.
The effect of Al2O3 content on the structure, electrical properties, magnetic properties, and interparticle exchange interactions of (Fe65Co35)1 − x(Al2O3)x films with Al2O3 volume fractions x ranging from 0 to 0.50 was systematically investigated. Among the films with x between 0 and 0.25, the lowest coercivity of 0.56 kA/m was achieved in the (Fe65Co35)0.82(Al2O3)0.18 film. This is ascribed to the strongest exchange interactions between the Fe65Co35 nanoparticles in this film. Combined with the microstructure analysis of the (Fe65Co35)1 − x(Al2O3)x films, the modified Herzer's model was extended to interpret the variation of the coercivity with x and analyze the effect of the exchange interactions between the Fe65Co35 nanoparticles on the magnetic softness. The remanence curves confirm the existence of the exchange interactions and reveal the evolution of the exchange interaction strength with Al2O3 content. 相似文献
15.
Gel formation was realized by adding citric acid to a solution of La(NO3)3·5H2O, Ca(NO3)2·4H2O, and Fe(NO3)2·9H2O. Perovskite-type (La1−xCax)FeO3 (0 ≤ x ≤ 0.2) was synthesized by firing the gel at 500 °C in air for 1 h. The crystallite size (D1 2 1) decreased with increasing x, while the specific surface area was 6.8-9.4 m2/g and independent of x. The XPS measurement of the (La1−xCax)FeO3 surface indicated that the Ca2+ ion content increased with increasing x, while the Fe ion content was independent of x. Catalytic activity for CO oxidation increased with increasing x. 相似文献
16.
The phase structure, microwave dielectric properties, and their stability with different annealing conditions have been investigated in (Li1/4Nb3/4) substituted ZrxSnyTizO4 system. The sintering temperature of ZrxSnyTizO4 ceramic was lowered from 1500 to 1140 °C by (Li1/4Nb3/4) substitution. Both X-ray diffraction (XRD) analysis and electron diffraction (ED) analysis revealed that the (Li1/4Nb3/4) substituted ZrxSnyTizO4 ceramic crystallized as the high-temperature disordered ZrTiO4 phase. As the content of Sn increased from 0.10 to 0.30, the permittivity of the (Zr1−xSnx)(Li1/4Nb3/4)0.4Ti0.6O4 ceramic decreased gradually from 35.5 to 31.5, the Qf value increased from 37,800 to 58,300 GHz, and TCF value shifted slightly from −4.5 to −33.0 ppm °C−1. Both the phase structure and microwave dielectric properties of (Zr1−xSnx)(Li1/4Nb3/4)0.4Ti0.6O4 ceramics were stable with annealing conditions. 相似文献
17.
Polycrystalline Sr2Fe1−xGaxMoO6 (0 ≤ x ≤ 0.6) materials have been synthesized by solid state reaction method and studied by neutron powder diffraction (NPD) and magnetization measurements. Rietveld analysis of the temperature dependent NPD data shows that the compounds crystallize in the tetragonal symmetry in the space group I4/m. The anti-site (AS) defects concentration increases with Ga doping, giving rise to highly B-site disordered materials. Ga doping at the Fe-site decreases the cell volume. The evolution of bond lengths and the cation oxidation states was determined from the Rietveld refinement data. The saturation magnetization and Curie temperature decreased with the increasing Ga content in the samples. Low temperature neutron diffraction data analysis and magnetization measurements confirm the magnetic interaction as ferrimagnetic in the sample. 相似文献
18.
Crystal structures of BiMn0.97Al0.03O3 (I) at 300 and 470 K and BiMn0.9Al0.1O3 (II) at 90 and 300 K were studied with synchrotron X-ray powder diffraction. The strong Jahn-Teller distortion, observed at 300 K in I and associated with orbital order, disappeared at 470 K completely for one site and partially for the second site. The Mn/Al-O distances were very close to each other in I at 470 K and in II at 90 and 300 K indicating that orbital order did not appear in II even at 90 K. Magnetic properties of I and II were investigated with specific heat, high-temperature dc magnetic susceptibility, and ac magnetic susceptibility using different driving ac and applied dc magnetic fields and different ac magnetic field frequencies. The anomaly on the specific heat associated with a magnetic transition was strongly suppressed in II compared with that of I and BiMnO3. 相似文献
19.
Boron tungsten bronzes BxWO3 (0.01 ≤ x ≤ 0.08) were synthesized by hybrid microwave method from mixtures of WO3 and amorphous boron powder. With the increase of boron content, the crystal structure of BxWO3 transforms from orthorhombic (x = 0.01) to tetragonal α (x = 0.048) and then to tetragonal β (0.07 ≤ x ≤ 0.08). The average size of crystallites is in the range of 1-10 μm. All samples show semiconducting behaviour in their temperature dependence of resistivity. The conduction behaviour above 80 K for samples with x = 0.01 and 0.08 can be explained using the variable-range hopping and thermally activated mechanism, respectively. Comparative experiments showed that boron bronze phases cannot be obtained by the microwave heating of pure WO3 powder or a mixture of B2O3 and WO3 under the same conditions. 相似文献
20.
CdSexTe1−x (0 ≤ x ≤ 0.4) ternary thin films have been deposited on quartz substrates at room temperature by a single source thermal evaporation. X-ray diffraction patterns and transmission electron microscope micrographs of these films showed that the films were of polycrystalline texture over the whole range studied and exhibit predominant cubic (zinc blende) structure with strong preferential orientation of the crystallites along (1 1 1) direction. Linear variation of the lattice constant with mole fraction x is observed obeying Vegard's law. The dependence of the optical constants, the refractive index n and extinction coefficient k, of the films on the mole fraction x was studied in the spectral range of 400-2500 nm. The normal dispersion of the refractive index of the films could be described using the Wemple-DiDomenco single-oscillator model. CdSexTe1−x thin films of different composition have two direct and indirect transitions corresponding to energy gaps and . The variation in either or with x indicates that this system belongs to the amalgamation type. The variation follows a subquadratic dependence and the bowing parameters were found to be 0.36 and 0.48 eV for the direct, and indirect energy gaps, respectively. Direct linear variation of the ratio N/m* with x is observed. 相似文献