共查询到20条相似文献,搜索用时 31 毫秒
1.
Yih-Chien Chen Sheng-Kai YangKuang-Chiung Chang 《Journal of Alloys and Compounds》2011,509(39):9518-9522
The microwave dielectric properties of La(Mg0.5−xNixSn0.5)O3 ceramics were examined with a view to their exploitation for mobile communication. The La(Mg0.5−xNixSn0.5)O3 ceramics were prepared by the conventional solid-state method at various sintering temperatures. The X-ray diffraction patterns of the La(Mg0.4Ni0.1Sn0.5)O3 ceramics revealed no significant variation of phase with sintering temperatures. Apparent density of 6.71 g/cm3, dielectric constant (?r) of 20.19, quality factor (Q × f) of 74,600 GHz, and temperature coefficient of resonant frequency (τf) of −85 ppm/°C were obtained for La(Mg0.4Ni0.1Sn0.5)O3 ceramics that were sintered at 1550 °C for 4 h. 相似文献
2.
Hai Jin Li Xiao Ying Qin Yi LiuDi Li Jin Lian Hu 《Journal of Alloys and Compounds》2011,509(8):3677-3681
Substitutional compounds Cr1−xNixSb2 (0 ≤ x ≤ 0.1) were synthesized, and the effect of Ni substitution on transport and thermoelectric properties of Cr1−xNixSb2 were investigated at the temperatures from 7 to 310 K. The results indicated that the magnitudes of the resistivity and thermopower of Cr1−xNixSb2 decreased greatly with increasing Ni content at low temperatures, owing to an increase in electron concentration caused by Ni substitution for Cr. Experiments also showed that the low-temperature lattice thermal conductivity of Cr1−xNixSb2 decreased substantially with increasing Ni content due to an enhancement of phonon scattering by the increased number of Ni atoms. As a result, the figure of merit, ZT, of lightly doped Cr0.99Ni0.01Sb2 was improved at T > ∼230 K. Specifically, the ZT of Cr0.99Ni0.01Sb2 at 310 K was approximately ∼29% larger than that of CrSb2, indicating that thermoelectric properties of CrSb2 can be improved by an appropriate substitution of Ni for Cr. 相似文献
3.
Yang-huan Zhang Bao-wei LiHui-ping Ren Feng Hu Guo-fang Zhang Shi-hai Guo 《Journal of Alloys and Compounds》2011,509(18):5604-5610
The nanocrystalline Mg2Ni-type Mg2Ni1−xCux (x = 0, 0.1, 0.2, 0.3, 0.4) alloys were synthesized by direct melt quenching technique. The structures of the as-cast and quenched alloys were investigated by XRD, SEM and HRTEM. The gaseous hydrogen storage kinetics of the alloys was measured using an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage kinetics of the alloys was tested by using constant current to charge and discharge the electrode. The results indicate that the substitution of Cu notably rendered the grain refinement of the as-cast alloys without altering the major phase Mg2Ni. All the as-quenched alloys exhibit a nanocrystalline structure without the presence of any amorphous phase. It is found that the substitution of Cu for Ni and rapid quenching significantly ameliorated the gaseous and electrochemical hydrogen storage kinetics of the nanocrystalline Mg2Ni1−xCux (x = 0-0.4) alloys. Furthermore, both the rapid quenching treatment and the Cu substitution results in a notable increase in the hydrogen diffusion coefficient (D) as well as the limiting current density (IL) but an obvious decline in the electrochemical impedance. 相似文献
4.
Yi-Jie Gu Yun-Bo ChenHong-Quan Liu Yan-Ming WangCui-Ling Wang Hui-Kang Wu 《Journal of Alloys and Compounds》2011,509(30):7915-7921
We report the synthesis of LiNi0.85−xCo0.15MnxO2 positive electrode materials from Ni0.85−xCo0.15Mnx(OH)2 and Li2CO3. XRD and XPS are used to study the effect of Mn-doping on the microstructures and oxidation states of the LiNi0.85−xCo0.15MnxO2 materials. The analysis shows that Mn-doping promotes the formation of a single phase. With increasing substitution of Mn ions for Ni ions, the lattice parameter a decreases, while the lattice parameters c and c/a increase. XPS revealed that the oxidation states of Ni, Co and Mn in LiNi0.85−xCo0.15MnxO2 compounds (where x = 0.1, 0.2 and 0.4) were +2/+3, +3 and +4. The substitution of Mn ions for Ni ions induces a decrease in the average oxidation state of Ni. Because the substitution of Mn for Ni ions is complex, the extent of the changes between the lattice parameter and LM-O differ. The occupation of Ni in Li sites is affected by the ordering of Mn4+ with Ni2+ and Mn4+ with Li+. 相似文献
5.
The phase relation, microstructure, Curie temperatures (TC), magnetic transition, and magnetocaloric effect of (Gd1−xErx)5Si1.7Ge2.3 (x = 0, 0.05, 0.1, 0.15, and 0.2) compounds prepared by arc-melting and then annealing at 1523 K (3 h) using purity Gd (99.9 wt.%) are investigated. The results of XRD patterns and SEM show that the main phases in those samples are mono-clinic Gd5Si2Ge2 type structure. With increase of Er content from x = 0 to 0.2, the values of magnetic transition temperatures (TC) decrease linearly from 228.7 K to 135.3 K. But the (Gd1−xErx)5Si1.7Ge2.3 compounds display large magnetic entropy near their transition temperatures in a magnetic field of 0-2 T. The maximum magnetic entropy change in (Gd1−xErx)5Si1.7Ge2.3 compounds are 24.56, 14.56, 16.84, 14.20, and 13.22 J/kg K−1 with x = 0, 0.05, 0.1, 0.15, and 0.2, respectively. 相似文献
6.
Ag-doped Ca3Co4O9 thin films with nominal composition of Ca3−xAgxCo4O9 (x = 0∼0.4) have been prepared on sapphire (0 0 0 1) substrates by pulsed laser deposition (PLD). Structural characterizations and surface chemical states analysis have shown that Ag substitution for Ca in the thin films can be achieved with doping amount of x ≤ 0.15; while x > 0.15, excessive Ag was found as isolated and metallic species, resulting in composite structure. Based on the perfect c-axis orientation of the thin films, Ag-doping has been found to facilitate a remarkable decrease in the in-plane electrical resistivity. However, if doped beyond the substitution limit, excessive Ag was observed to severely reduce the Seebeck coefficient. Through carrier concentration adjustment by Ag-substitution, power factor of the Ag-Ca3Co4O9 thin films could reach 0.73 mW m−1 K−2 at around 700 K, which was about 16% higher than that of the pure Ca3Co4O9 thin film. 相似文献
7.
R. SeemaC.S. Suchand Sandeep Reji PhilipNandakumar Kalarikkal 《Journal of Alloys and Compounds》2011,509(34):8573-8576
Sr2CeO4 blue phosphor has been prepared by the solid-state reaction method. The X-ray diffraction (XRD) study confirms the structure of the system to be orthorhombic. High resolution electron transmission microscopy reveals that Sr2CeO4 prepared by the solid state reaction method is composed of elongated spherical structures of length ∼0.2-0.6 μm and width ∼90-150 nm. The excitation spectrum shows a broad band which peaks at 275 nm. The emission spectrum shows a broad band which peaks at 467 nm when excited at 275 nm. The emission band is assigned to the energy transfer between the molecular orbital of the ligand and charge transfer (CT) state of the Ce4+ ion. The Commission International de l’Eclairage (CIE) co-ordinates are x = 0.15, and y = 0.23. The nonlinear absorption behavior of Sr2CeO4 has been investigated using the open aperture z-scan technique. The calculated effective two-photon absorption coefficient shows that the Sr2CeO4 blue phosphor is a promising optical limiting material. 相似文献
8.
The formation of impurity LixNi1−xO when synthesizing spinel LiNi0.5Mn1.5O4 using solid state reaction method, and its influence on the electrochemical properties of product LiNi0.5Mn1.5O4 were studied. The secondary phase LixNi1−xO emerges at high temperature due to oxygen deficiency for LiNi0.5Mn1.5O4 and partial reduction of Mn4+ to Mn3+ in LiNi0.5Mn1.5O4. Annealing process can diminish oxygen deficiency and inhibit impurity LixNi1−xO. The impurity reduces the specific capacity of product, but it does not have obvious negative effect on cycle performance of product. The capacity of LiNi0.5Mn1.5O4 that contains LixNi1−xO can deliver about 120 mAh g−1. 相似文献
9.
(1 − x)ZnMoO4-xTiO2 (x = 0.0, 0.05, 0.158, 0.25, and 0.35) composite ceramics were synthesized by the conventional solid state reaction process. The sintering behavior, phase composition, chemical compatibility with silver, and microwave dielectric properties were investigated. All the specimens can be well densified below 950 °C. From the X-ray diffraction analysis, it indicates that the triclinic wolframite ZnMoO4 phase coexists with the tetragonal rutile TiO2 phase, and it is easy for silver to react with ZnMoO4 to form Ag2Zn2(MoO4)3 phase and hard to react with TiO2. When the volume fraction of TiO2 (x value) increasing from 0 to 0.35, the microwave dielectric permittivity of the (1 − x)ZnMoO4-xTiO2 composite ceramics increases from 8.0 to 25.2, the Qf value changes in the range of 32,300-43,300 GHz, and the temperature coefficient τf value varies from −128.9 to 157.4 ppm/°C. At x = 0.158, the mixture exhibits good microwave dielectric properties with a ?r = 13.9, a Qf = 40,400 GHz, and a τf = +2.0 ppm/°C. 相似文献
10.
Hydrogen storage characteristics of nanocrystalline and amorphous Mg2Ni-type alloys prepared by melt spinning 总被引:1,自引:0,他引:1
Yang-huan Zhang Feng Hu Zhi-gang Li Ke Lü Shi-hai GuoXin-lin Wang 《Journal of Alloys and Compounds》2011,509(2):294-300
In order to improve the hydrogen storage characteristics of the Mg2Ni-type alloys, Ni in the alloy is partially substituted by element Mn, and melt-spinning technology is used for the preparation of the Mg2Ni1−xMnx (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys. The microstructures of the as-cast and spun alloys are characterized by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinetics of the alloys are measured by an automatically controlled Sieverts apparatus. The electrochemical performances are tested by an automatic galvanostatic system. The results show that the as-spun Mn-free alloy holds typical nanocrystalline structure, whereas the as-spun alloys containing Mn displays a nanocrystalline and amorphous structure. The hydrogen absorption and desorption capacities and kinetics of the alloys increase with rising spinning rate. Additionally, melt spinning markedly improves the electrochemical hydrogen storage capacity and cycle stability of the alloys containing Mn. With an increase in the spinning rate from 0 (As-casts is defined as spinning rate of 0 m/s) to 30 m/s, the discharge capacity of the (x = 0.3) alloy mounts up from 92.3 to 211.1 mAh/g, and its capacity retaining rate at 20th charging and discharging cycle grows from 36.21% to 76.02%. 相似文献
11.
Yang-huan Zhang Bao-wei LiHui-pin Ren Xiao-xia Ding Xiao-gang Liu Le-le Chen 《Journal of Alloys and Compounds》2011,509(6):2808-2814
In order to improve the hydrogen storage kinetics of the Mg2Ni-type alloys, Ni in the alloy was partially substituted by element Co, and melt-spinning technology was used for the preparation of the Mg2Ni1−xCox (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys. The structures of the as-cast and spun alloys are characterized by XRD, SEM and TEM. The hydrogen absorption and desorption kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage kinetics of the as-spun alloys is tested by an automatic galvanostatic system. The hydrogen diffusion coefficients in the alloys are calculated by virtue of potential-step method. The electrochemical impedance spectrums (EIS) and the Tafel polarization curves are plotted by an electrochemical workstation. The results show that the substitution of Co for Ni notably enhances the glass forming ability of the Mg2Ni-type alloy. Furthermore, the substitution of Co for Ni, instead of changing major phase Mg2Ni, leads to forming secondary phases MgCo2 and Mg. Both the melt spinning treatment and Co substitution significantly improve the hydrogen absorption and desorption kinetics. The high rate discharge ability, the hydrogen diffusion coefficient and the limiting current density of the alloys significantly increase with raising both the spinning rate and the amount of Co substitution. 相似文献
12.
The kinetic mechanisms of dehydriding reaction in La0.8M0.2Ni5 and LaNi4.5T0.5 were comparatively investigated by the Chou model and the first order model, and the former was superior to the latter from the comparison of theoretical calculated results and experimental data. According to the characteristic time (tc) in the Chou model, substituting La (tc = 71.36 s) with Ce (tc = 35.64 s), Nd (tc = 30.82 s) and Pr (tc = 28.86 s) increased the dehydriding reaction rate, but partial substitution of Ni (tc = 71.36 s) with Co (tc = 102.29 s), Fe (tc = 116.70 s) and Cu (tc = 120.62 s) decreased the hydrogen desorption reaction rate. The Chou model was also used to discuss the effect of different amount of Ni substituted with Fe and Co. The dehydriding reaction rates of La(Ni1−xFex)5 increased with x leveling from 0 to 0.20 but decreased with x increasing from 0.20 to 0.30, while that of LaNi5−yCoy decreased with increasing the amount of Co from 0 to 3.00. In addition, the Chou model was successfully applied to predicting the kinetic properties of LaNi4.8Sn0.2 at 40 °C and 60 °C, which exhibited an excellent agreement with the experimental data. 相似文献
13.
KSrPO4:Tb3+ phosphors were prepared by a solid-state method and their photoluminescence properties were investigated under vacuum ultraviolet excitation. In the excitation spectrum monitoring at 544 nm, the band in the region of 120-162 nm can be attributed to be the overlap of host absorption and charge transfer transition of O2− → Tb3+, and the band ranging from 162 to 300 nm was assigned to the f-d transition of Tb3+. The photoluminescence spectrum shows that the phosphors exhibited a strong green emission around 544 nm corresponding to the 5D4 → 7F5 transition of Tb3+ under the excitation of 147 nm. Optimal emission intensity was obtained when x = 7% in KSr1-xPO4:xTb3+ and the luminescent chromaticity coordinates were calculated to be (x = 0.317, y = 0.522) for KSr0.93PO4:7%Tb3+. 相似文献
14.
B. Pato-DoldánM. Sánchez-Andújar S. Castro-García M.A. Señarís-Rodríguez 《Journal of Alloys and Compounds》2011,509(5):1529-1533
We have prepared polycrystalline single-phase ACo2+xRu4−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. 相似文献
15.
Shao-An YanYee-Shin Chang Weng-Sing Hwang Yen-Hwei ChangMasahiro Yoshimura Chii-Shyang Hwang 《Journal of Alloys and Compounds》2011,509(19):5777-5782
Color-tunable phosphors BaLa2−xEuxWO7 were synthesized via a solid-state reaction. The absorption, excitation, emission and decay curves were obtained to study the luminescence properties. The experimental results indicate that BaLa2−xEuxWO7 phosphors have two regions in the excitation spectra: one is assigned to the charge-transfer state (CTS) band at about 338 nm, and the other is assigned to the intra-4f transitions at 360-600 nm. The emission spectra of BaLa2−xEuxWO7 phosphors excited at 395 nm exhibit a series of sharp peaks, which are attributed to the 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions. Luminescence from higher excited states, such as 5D1, 5D2, and 5D3, were also observed at low Eu3+ concentration. The optimal emission intensity of 5D0 → 7F2 red emission is at x = 0.4 (BaLa1.6Eu0.4WO7). The chromaticity coordinates of BaLa2−xEuxWO7 phosphors vary with Eu3+ content from white, orange-red, to red, making it a candidate for a white-light-emitting phosphor in UV-LEDs. 相似文献
16.
Alloys from the solid solution Ce1−xThxPt3Si (x = 0.0, 0.02, 0.04, 0.08, 0.1, 0.2 and 1.0) were prepared by arc-melting. X-ray Rietveld powder analyses revealed that alloys in the compositional range 0 ≤ x ≤ 0.2 crystallize with the CePt3B-type with a random distribution of Ce and Th atoms in positions 1(b) (1/2, 1/2, z) of the noncentrosymmetric space group P4mm. Th-doping results in a rapid suppression of the superconductivity. The alloy with x = 0.02 shows the onset of superconducting state at Tc = 400 mK, while that with x = 0.04 remains in normal metallic state at least down to 70 mK. 相似文献
17.
The phase relation, microstructural, hysteresis, Curie temperature, and magnetocaloric effects of LaFe11.6Si1.4Bx (x = 0.1, 0.2, 0.3, 0.4, and 0.5) prepared by arc-melting and then annealed at 1373 K (1.5 h) + 1523 K (5 h) were investigated. It was found that the main phase is NaZn13-type phase, the impurity phases include α-Fe, Fe2B, and small amount of La5Si3. The boron atom can dissolve into the crystal lattice of LaFe11.6Si1.4Bx to form interstitial solid solution, but the content of solid solution is not up to x = 0.5. For LaFe11.6Si1.4Bx (x = 0.1, 0.3, and 0.5) compounds, the Curie temperature TC increases from 190.6 to 198.3 K with the increasing of B content from x = 0.1 to 0.5. The first order magnetic transition behavior becomes weaker and magnetic entropy change ΔSM (T, H) drops with the increasing of B content, respectively. However, ΔSM (T, H) still remains a large value, 11.18 J/kg K, when x reaches to 0.5 at 0-2 T. An attractive feature is that both thermal and magnetic hysteresis can be reduced remarkably by introducing B. The maximum magnetic hysteresis loss near TC drops from 22.52 to 4.95 J/kg when the content of B increases from x = 0.1 to 0.5. 相似文献
18.
NixMn0.8−xMg0.2Fe2O4; 0.0≤ x ≤0.40 was prepared by standard ceramic technique, presintering was carried out at 900 °C and final sintering at 1200 °C with heating/cooling rate 4 °C/min. X-ray diffraction analyses assured the formation of the samples in a single phase spinel cubic structure. The calculated crystal size was obtained in the range of 75-130 nm. A slight increase in the theoretical density and decrease in the porosity was obtained with increasing the nickel content. This result was discussed based on the difference in the atomic masses between Ni (58.71) and Mn (54.938). IR spectral analyses show four bands of the spinel ferrite for all the samples. The conductivity and dielectric loss factor give nearly continuous decrease with increasing Ni-content. This was discussed as the result of the significant role of the multivalent cations, such as iron, nickel, manganese, in the conduction mechanism. Anomalous behavior was obtained for the sample with x = 0.20 as highest dielectric constant, highest dielectric loss and highest conductivity. This anomalous behavior was explained due to the existence of two divalent cations on B-sites with the same ratio, namely, Mg2+ and Ni2+. 相似文献
19.
Hengzhi ChenBin Yang Mingfu ZhangFeiyan Wang Kokwai CheahWenwu Cao 《Journal of Alloys and Compounds》2011,509(17):5364-5367
Lanthanum doped Bi3TiNbO9 thin films (LBTN-x, La3+ contents x = 5%, 15%, 25% and 35 mol.%) with layered perovskite structure were fabricated on fused silica by pulsed laser deposition method. Their linear and nonlinear optical properties were studied by transmittance measurement and Z-Scan method. All films exhibit good transmittance (>55%) in visible region. For lanthanum doping content are x = 5%, 15% and 25 mol.%, the nonlinear absorption coefficient of LBTN-x thin films increases with the La3+ content, then it drops down at x = 35 mol.% when the content of La3+ in (Bi2O2)2+ layers is high enough to aggravate the orthorhombic distortion of the octahedra. We found that, 25 mol.% is the optimal La3+ content for LBTN-x thin films to have the largest nonlinear absorption coefficient making the LBTN-x film a promising candidate for absorbing-type optical device applications. 相似文献
20.
Adul Harnwunggmoung Ken Kurosaki Yuji OhishiHiroaki Muta Shinsuke Yamanaka 《Journal of Alloys and Compounds》2011,509(3):1084-1089
In order to enhance the thermoelectric (TE) properties of CoSb3, we tried to reduce the lattice thermal conductivity (κlat) by filling Tl into the voids and substitution of Rh for Co. We prepared polycrystalline samples of Tlx(Co1−yRhy)4Sb12 (x = 0, 0.05, 0.10, 0.15, 0.20 and y = 0.1, 0.2) and examined their TE properties from room temperature to 750 K. All the samples indicated negative values of the Seebeck coefficient (S). Both the electrical resistivity and the absolute values of the S decreased with increasing the Tl-filling ratio. The Tl-filling and Rh substitution reduced the κlat, due to the rattling and the alloy scattering effects. The minimum value of the κlat was 1.54 W m−1 K−1 at 550 K obtained for Tl0.20(Co0.8Rh0.2)4Sb12. Tl0.20(Co0.8Rh0.2)4Sb12 exhibited the best TE performance; the maximum value for the dimensionless figure of merit ZT was 0.58 at around 600 K. 相似文献