共查询到20条相似文献,搜索用时 46 毫秒
1.
Yongfang Shi Xi Chen Jingsa Han Hui Ma Xiaoxia Li Xiaojing Yang Xinhua Zhao 《Journal of solid state chemistry》2009,182(8):2030-2035
A systematical study on cubic ZrW2−xMoxO8 (x=0.73, 0.53, 0.33, 0.11) solid solutions reveals that their temperature-dependent phase transition behaviors are related to the Mo fraction x. A phase diagram of cubic ZrW2−xMoxO8 solid solutions has been drawn over a wide temperature range (298–1473 K) on the basis of the temperature-dependent phase transition behaviors observed. 相似文献
2.
F. Nakagomi S.W. da Silva V.K. Garg A.C. Oliveira P.C. Morais A. Franco Jr. 《Journal of solid state chemistry》2009,182(9):2423-2429
The influence of the Mg-content on the structural and magnetic properties of cubic MgxFe3−xO4 nanoparticles prepared by combustion reaction was investigated using X-ray diffraction, transmission electron microscopy (TEM), Mössbauer spectroscopy, and Raman spectroscopy. Lattice parameter, nanoparticle size, and cation (Mg2+, Fe3+) distribution were quantified as a function of the Mg-content in the range 0.5≤x≤1.5. We found a mixed-like spinel structure at the smaller x-value end whereas the inverse-like spinel structure dominates samples with larger x-values. Moreover, in the x-value range investigated (0.5≤x≤1.5) we found no change in the quadrupole splitting and isomer shift values, though the hyperfine field decreases as the x-value increases. The splitting of the A1g Raman mode was used to both quantify the Mg2+/Fe3+ contents in the tetrahedral site and obtain the cation distribution in the MgxFe3−xO4 structure. The cation distribution obtained from the Raman data is in very good agreement with the cation distribution obtained from the Mössbauer data. 相似文献
3.
The solid solution of YMn1−xFexO3 (x=0.0, 0.1, 0.2, 0.3, 0.5, 1.0) was synthesized from the citrate precursor route. The hexagonal crystal structure related to YMnO3 was stable for x?0.3. Rietveld refinement was carried out on the composition for x=0.3 and was refined to a major hexagonal phase (∼97%) with 3% of orthorhombic Y(Fe/Mn)O3 phase. The a-axis lattice constant increases and the c-axis lattice constant decreases with x for x?0.2. The increase in the c-axis lattice constant at x=0.3 could be due to the doping of significant amount of d5 ion (high spin Fe3+ ion) in a trigonal bipyramidal crystal field. The detailed structural, magnetic and dielectric properties are discussed. 相似文献
4.
The magnetic and electric transport properties of La1−xBaxCoO3 (0<x≤0.50) have been studied systematically. Two effects of substitution divalent ions on the spin-state transition of Co3+ have been differentiated for the substitution of Ba2+ for La3+ in La1−xBaxCoO3. The first is the transition from low-spin state to high-spin state due to lattice expansion, and the second is the transition from low-spin state to intermediate-spin state caused by the strong hybridization between ligand (oxygen) 2p and Co 3d orbital with introduction of holes in the oxygen 2p orbital. Based on the two different spin-state transition mechanisms and experimental results, a phase separation model has been developed and a very detailed magnetic and electric phase diagram of La1−xBaxCoO3 has been constructed. 相似文献
5.
6.
The crystal structure of Sr4Mn2NiO9 has been refined on single crystal. This phase belongs to the series A1+x(A′xB1–x)O3 (x=1/3) related to the 2H-hexagonal perovskite. The structure contains transition metals in chains of oxide polyhedra (trigonal prisms and octahedra); neighboring chains are separated from each other by the Sr atoms. The sequence of the face sharing polyhedra along the chains is two octahedra + one trigonal prism. Mn occupies the octahedra and Ni is disordered in the trigonal prism with ≈80% in the pseudo square faces of the prism and ≈20% at the centre. This result has been confirmed by XANES experiments at Mn K and Ni K edges, respectively. Sr4Mn2NiO9 is antiferromagnetic with a Néel temperature at T=3 K. The Curie constant measured at high temperature is in good agreement with ≈80% of the Ni2+ ions in the spin state configuration S=0. 相似文献
7.
B. Dabrowski E.N. Caspi S. Kolesnik J. Mais 《Journal of solid state chemistry》2005,178(11):3453-3460
We report the synthesis of SrMn1−xGaxO3−δ perovskite compounds and describe the dependence of their phase stability and structural and physical properties over extended cation and oxygen composition ranges. Using special synthesis techniques derived from thermogravimetric measurements, we have extended the solubility limit of random substitution of Ga3+ for Mn in the cubic perovskite phase to x=0.5. In the cubic perovskite phase the maximum oxygen content is close to 3−x/2, which corresponds to 100% Mn4+. Maximally oxygenated solid solution compounds are found to order antiferromagnetically for x=0-0.4, with the transition temperature linearly decreasing as Ga content increases. Increasing the Ga content introduces frustration into the magnetic system and a spin-glass state is observed for SrMn0.5Ga0.5O2.67(3) below 12 K. These properties are markedly different from the long-range antiferromagnetic order below 180 K observed for the layer-ordered compound Sr2MnGaO5.50 with nominally identical chemical composition. 相似文献
8.
Qingdi Zhou 《Journal of solid state chemistry》2005,178(11):3589-3594
Synchrotron X-ray and neutron powder diffraction were used to investigate the formation, structure and bonding in the double perovskite Ba2−xSrxTbIrO6 solid solutions. The results showed that these oxides all exhibit ordering of the Tb and Ir cations in a double perovskite-type structure. Three distinct structural types differing in symmetry and/or valence states were formed depending on the precise Ba:Sr ratio on the perovskite A site; x?0.3 cubic () with Tb4+ and Ir4+; 0.4?x?1.0 cubic () with Tb3+ and Ir5+ and x?1.2 monoclinic (P21/n) with Tb3+ and Ir5+. The transitions between these appear to be first order in nature. 相似文献
9.
C. Deviannapoorani L. Dhivya S. Ramakumar R. Murugan 《Journal of Sol-Gel Science and Technology》2012,64(2):510-514
Preparation of lithium garnet Li7La3Zr2O12 (LLZ) in cubic phase by solid state method requires high temperature sintering around 1,200 °C for 36 h in Al2O3 crucible with intermittent grinding. Synthesis of LLZ in cubic phase at lower temperatures by wet chemical methods was reported earlier, however that decompose at high temperature around 850 °C. In this work we report the systematic studies on synthesis of garnet structured electrolytes by modified sol–gel method by the simultaneous substitution of Li+ and Y3+ for Zr4+ according to the formulae Li7+x La3Y x Zr2-x O12 (x = 0, 0.1, 0.2, 0.3 and 0.4). The present investigation revealed that the cubic garnet phase is obtained at much lower temperature for Li7La3Zr2O12 and the simultaneous increase of both Li+ and Y3+ in Li7+x La3Y x Zr2-x O12 requires slightly higher sintering temperatures for the formation of cubic garnet phase. SEM micrographs of the Li7+x La3Y x Zr2-x O12 (x = 0, 0.1, 0.2, 0.3 and 0.4) annealed at minimum sintering temperature required for the formation of cubic garnet phase revealed the increase in grain size and relatively dense structure with increase of x in Li7+x La3Y x Zr2-x O12. 相似文献
10.
C. Ma J.-Q. Yan K.W. Dennis R.W. McCallum X. Tan 《Journal of solid state chemistry》2009,182(11):3013-3020
Polycrystalline samples of the Lu1−xLaxMn2O5 solid solution system were synthesized under moderate conditions for compositions with x up to 0.815. Due to the large difference in ionic size between Lu3+ and La3+, significant changes in lattice parameters and severe lattice strains are present in the solid solution. This in turn leads to the composition dependent thermal stability and magnetic properties. It is found that the solid solution samples with x≤0.487 decompose at a single well defined temperature, while those with x≥0.634 decompose over a temperature range with the formation of intermediate phases. For the samples with x≤0.487, the primary magnetic transition occurs below 40 K, similar to LuMn2O5 and other individual RMn2O5 (R=Bi, Y, and rare earth) compounds. In contrast, a magnetic phase with a 200 K onset transition temperature is dominant in the samples with x≥0.634. 相似文献
11.
Mössbauer spectra of the Fe1+xV2−xO4 spinel solid solutions are taken to investigate the cation distribution. Room temperature spectra can be interpreted by assuming that the cation distribution is represented approximately as Fe2+[Fe3+xV3+2−x]O4 for 0 x 0.35 and Fe3+[Fe2+Fe3+x−1V3+2−x]O4 for 1 x 2 and the ionic valence arrangement changes from the 2-3-3 type (Fe2+[Fe3+xV3+2−x]O4) to the 3-2-3 one (Fe3+[Fe2+V3+]O4) in the range 0.35 x 1. Fe2VO4 is found to be 3-2-3 spinel, Fe3+[Fe2+V3+]O4. Its paramagnetic spectrum at 473°K is, however, composed of a broad single line with isomer shift value of 0.61 mm/sec relative to stainless steel, in which the line splitting due to the ferric and ferrous ions is rendered indistinguishable. 相似文献
12.
With the exception of FeRh2S4, powder samples of all systems studied have been obtained as spinel phase without essential impurities. The lattice constants follow Vegard's law. From the Seebeck coefficients and the Mössbauer spectra the valence distribution Cu1+1−xFe2+2x−1Fe3+1−x[Me3+2]X2−4 is derived for 0.5 x 1, while there is only Fe3+ present for 0 < x 0.5. Samples with the overall composition FeRh2S4 contain mostly Rh2S3 and iron sulfide phases, but less than 20% of a spinel phase. 相似文献
13.
A new complete solid solution of NASICON-type compounds between LiZr2(PO4)3 and La1/3Zr2(PO4)3 was evidenced with the general formula Li1−xLax/3Zr2(PO4)3 (0?x?1). These phases were synthesized by a complex polymerizable method and structurally characterized from Rietveld treatment of their X-ray and neutron powder diffraction data. This solid solution results from the substitution mechanism Li+→1/3La3++2/3□ leading to an increase of the vacancies number correlated to an increase of the La content. According to this substitution mechanism, the general formula can then be written Li1−xLax/3□2x/3Zr2(PO4)3 (0?x?1) in order to underline the correlation between the La content and the vacancies rate. For all the compounds, the structure is clearly related to that of the NASICON family with three crystallographic domains evidenced. For 0?x?0.5, all the members adopt at high temperature the typical NASICON-type structure (s.g. R3¯c), while at lower temperature, their structure distorts to a triclinic form (s.g. C 1¯), as observed for LiZr2(PO4)3 prepared above 1100 °C. Moreover, in this domain, the reversible transition is clearly soft and the transition temperature strongly depends of the x value. For 0.6?x?0.9, the compounds crystallize in a rhombohedral cell (s.g. R3¯), while for x=1, the phase La1/3Zr2(PO4)3 is obtained (s.g. P3¯, Z=6, a=8.7378(2) Å, c=23.2156(7) Å).This paper is devoted to the structure analysis of the series Li1−xLax/3Zr2(PO4)3 (0?x?1), from X-ray and neutron powder thermo diffraction and transmission electron microscopy (TEM) studies. 相似文献
14.
The new ternary phases Zr4−xTa1+xGe4 (0.1<x<0.4) and Zr2+xTa3−xGe4 (0.1<x<1.1) were prepared from the elements by arc melting and subsequent induction heating at 1400–1450°C. Single-crystal X-ray diffraction was used to determine their structures and to refine mixed site occupancies. Zr4−xTa1+xGe4 was found to crystallize in the monoclinic space group P21/c (structure type: U2Mo3Si4) and the compound Zr2−xTa3−xGe4 shows orthorhombic symmetry (space group Pnma, structure type: Sm5Ge4). The close structural relationship between the two structures is discussed. Both phases exhibit pronounced differential fractional site occupancy of Ta and Zr on the metal sites and considerable composition ranges. Extended Hückel calculations were performed for various site occupancy models and Mulliken overlap populations for the different lattice sites of each structure were calculated for these models. The correlation of the cumulated Mulliken overlap populations and the atomic orbital populations with the actual site occupancies is discussed. 相似文献
15.
Kyung-Wan Nam Won-Sub Yoon Karim Zaghib Kyung Yoon Chung Xiao-Qing Yang 《Electrochemistry communications》2009,11(10):2023-2026
How the structural changes take place in LiMnyFe1−yPO4-type cathode materials during lithium extraction/insertion is an important issue, especially on if they go through the single-phase reaction (i.e., solid solution reaction) or the two-phase reaction regions. Here we report the studies on the phase transition behaviors of a carbon coated Li1−xMn0.5Fe0.5PO4 (CLi1−xMn0.5Fe0.5PO4, 0.0 x 1.0) sample during the first charge using in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) techniques. The combination of in situ XAS and XRD results clearly identify two two-phase coexistence regions at two voltage plateaus of 3.6 (Fe2+/Fe3+) and 4.2 V (Mn2+/Mn3+) and a narrow intermediate region which proceeds via single-phase reaction in between two two-phase regions. In addition, simultaneous redox reactions of Fe2+/Fe3+ and Mn2+/Mn3+ in the narrow single-phase region are reported and discussed for the first time. 相似文献
16.
Effect of Transition Metals (Cu, Co and Fe) on the Autothermal Reforming of Methane over Ni/Ce0.2Zr0.1Al0.7Oδ Catalyst
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Xinfa Dong Xiulan Cai Yibing Song Weiming Lin 《天然气化学杂志》2007,16(1):31-36
The transition metals (Cu, Co, and Fe) were applied to modify Ni/Ce0.2Zr0.1 Al0.7Oδcatalyst. The effects of transition metals on the catalytic properties of Ni/Ce0.2Zr0.1 Al0.7Oδautothermal reforming of methane were investigated. The Ni-supported catalysts were characterized by XRD, TPR and XPS. Tests in autothermal reforming of methane to hydrogen showed that the addition of transition metals (Cu and Co) significantly increased the activity of catalyst under the conditions of lower reaction temperature, and Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδwas found to have the highest conversion of CH4 among all catalysts in the operation temperatures ranging from 923 K to 1023 K. TPR, XRD and XPS measurements indicated that the cubic phases of CexZr1-xO2 solid solution were formed in the preparation process of catalysts. Strong interaction was found to exist between NiO and CexZr1-xO2 solid solution. The addition of Cu improved the dispersion of NiO, inhibited the formation of NiAl2O4, and thus significantly promoted the activity of the catalyst Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδ. 相似文献
17.
掺杂Zr4+对纳米Au/TiO2催化剂结构和性能的影响 总被引:1,自引:0,他引:1
采用氨水反滴加沉淀法合成了Zr4+掺杂的系列TiO2载体,以尿素溶液为沉淀剂,用沉积-沉淀法制备负载金催化剂。运用N2吸附-脱附(BET)、X射线衍射(XRD)、X射线荧光(XRF)、高分辨电镜(HR-TEM)和氨吸附红外光谱(NH3-IR)等技术对催化剂的结构与形貌进行了表征,并在色谱-微反应装置上考察了催化剂对CO氧化反应的活性。结果表明:(1)少量的Zr4+掺杂可形成锐钛矿型固溶体,且载体的比表面积增大;随着Zr4+掺杂量增加至10%以上,载体逐渐向无定形转变,同时比表面积急剧增大。(2)保持规整锐钛矿晶相的Zr4+掺杂载体,其表面Lewis酸位占有率较高,且具备结构缺陷,而无定形载体表面的Lewis酸位占有率大幅度降低。(3)载体表面的Lewis酸位以及结构缺陷有利于增强载体对Au颗粒的锚定作用,从而减弱焙烧过程中的颗粒聚集。(4)少量Zr4+掺杂入TiO2载体中,可以提高Au颗粒的抗烧结能力,焙烧所得的Au颗粒尺寸较小(3.63 nm),且表现出优异的催化活性,在常温下就可以将CO完全氧化。 相似文献
18.
采用固相球磨法制备了K+掺杂双钙钛矿Cs2AgInCl6纳米材料,该方法无需配体辅助,绿色环保。通过X射线衍射谱和拉曼光谱对晶体结构进行研究,通过激发光谱、发射光谱和时间分辨光谱对其发光性能进行研究。结果表明,Cs2AgInCl6为立方晶体,属于Fm3m空间群,由于宇称禁戒跃迁,其荧光量子产率(PLQY)低,小于0.1%。低于60%的K+掺杂主要取代Ag+的位置,引起Cs2AgInCl6的晶格膨胀,消除了晶格结构的反演对称性,打破了宇称禁戒跃迁,掺杂后Cs2AgInCl6的光致发光强度显著增强。K+的最佳掺杂比例为40%,Cs2Ag0.6K0.4InCl6发出中心波长为640 nm,半高宽为180 nm,平均荧光寿命达到29.2 ns,PLQY达到10.5%。当K+掺杂比例超过60%,K+开始取代Cs+的位置,产物发生相变,出现立方相的Cs2-xK1+x-yAgyInCl6和单斜相的Cs2-xK1+xInCl6产物,这些产物由于强电子-声子耦合,非辐射复合占据主导地位。 相似文献
19.
V. Grover 《Journal of solid state chemistry》2004,177(11):4197-4204
The phase relations in the CeO2-Gd2O3-ZrO2 system have been established after slowly cooling the samples from 1400 °C. Ceria has been used as a surrogate material in place of plutonia. About 80 compositions in Zr1−xGdxO2−x/2, Ce1−xGdxO2−x/2, Ce1−xZrxO2.00, (Zr0.5Ce0.5)1−xGdxO2−x/2, (Ce0.5Gd0.5)1−xZrxO1.75+x/4, (Zr0.5Gd0.5)1−xCexO1.75+x/4, and (Ce0.8Zr0.2)xGd1−xO1.5+x/2 were prepared by a three steps heating protocol. Based on the refinement of the XRD data, several phase regions namely; cubic fluorite type solid solution, C-type solid solution, and various biphasic regions could be delineated. This system showed the existence of a very wide cubic phase field. About 17.5 mol% GdO1.5 was found to fully stabilize the cubic zirconia. On the other hand ceria did not stabilize the cubic zirconia. The anion-excess gadolinia, i.e., Gd1−xCexO1.5+x was found to retain the C-type lattite unlike pure gadolinia. The ternary phase relations were mainly characterized by the presence of wide homogeneity ranges of fluorite type or C-type phases. 相似文献
20.
A series of Ba1-xSrxTi1-yZryO3 (0≤x≤0.5, 0≤y≤0.4) and BA1?xZnxTi1?ySnyO3 (0≤x≤0.3, 0≤y≤0.3) solid solutions were synthesized by low-temperature/low-pressure hydrothermal method below 170°C, 0.8
MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible
solid solutions based on BaTiO3. Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size
of 70 nm in diameter. The sintered ceramics of those powders doped by Sr2+ and Zr4+ or Zn2+ and Sn4+ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO3 phase at room temperature. 相似文献