UV absorption properties of ceria-modified compositions within the fluorite-type solid solution CeO2-Y6WO12

A new fluorite-type solid solution domain has been evidenced in the system (1−x) CeO₂−x/7 Y₆WO₁₂□₂ using the amorphous citrate route. All the studied phases (0?x?1) crystallize in a cubic-type symmetry. Diffuse reflectance spectra reveal a strong optical absorption between 380 and 400 nm. All substituted compositions spectral selectivities are estimated suitable for application as inorganic UV absorbers. The non linear variation observed in the optical gap values between Y₆WO₁₂ and CeO₂ is attributed to the presence of the cerium 4f-block band. Additionally, Time Resolved Microwave Conductivity (TRMC) experiment and phenol photodegradation analyses carried out on the Ce_0.81Y_0.16W_0.03O_1.95□_0.05 (x=0.19) composition do not indicate any photocalatytic activity for this material.     

Optical properties of CeBO3 and CeB3O6 compounds: first-principles calculations and experimental results

The cerium borates o-CeBO₃, m-CeBO₃ and CeB₃O₆ have been shown to be isostructural to their lanthanum derivatives. From diffuse reflectance, electron energy loss spectroscopy (EELS) and band structure calculations, it has been evidenced that a Ce³⁺ 4f-5d transition is responsible for weak absorption peaks around 3.5 eV while the O2p-Ce5d charge transfer gives rise to a strong absorption around 7 eV. Starting from self-consistent full potential LAPW calculations, the dielectric tensors of the three compounds were computed and compared to experimental data. It results in a satisfactory fit between the observed and the calculated extinction coefficient k and the index of refraction n.     

Phase relation studies in the CeO2-Gd2O3-ZrO2 system

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 Zr_1−xGd_xO_2−x/2, Ce_1−xGd_xO_2−x/2, Ce_1−xZr_xO_2.00, (Zr_0.5Ce_0.5)_1−xGd_xO_2−x/2, (Ce_0.5Gd_0.5)_1−xZr_xO_1.75+x/4, (Zr_0.5Gd_0.5)_1−xCe_xO_1.75+x/4, and (Ce_0.8Zr_0.2)_xGd_1−xO_1.5+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% GdO_1.5 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., Gd_1−xCe_xO_1.5+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.     

Characterization and physical properties of Li2O-CaF2-P2O5 glass ceramics with Cr2O3 as a nucleating agent—Physical properties

In this paper, studies on various physical properties, viz., dielectric properties (dielectric constant, loss tan δ, a.c. conductivity σ) over a wide range of frequency and temperature, optical absorption, ESR at liquid nitrogen temperature and magnetic susceptibility at room temperature of Li₂O-CaF₂-P₂O₅: Cr₂O₃ glass ceramics, have been reported. The optical absorption, ESR and magnetic susceptibility studies indicate that the chromium ions exist in Cr⁵⁺, Cr⁴⁺ and Cr⁶⁺ states in addition to Cr³⁺ state in these samples. The dielectric constant and loss variation with the concentration of Cr₂O₃ have been explained on the basis of space charge polarization mechanism. The dielectric relaxation effects exhibited by these samples have been analysed by a graphical method and the spreading of dielectric relaxation has been established. The a.c. conductivity in the high-temperature region seems to be connected both with electronic and ionic movements.     

Effects of firing schedule on solubility limits and transport properties of ZrO2-TiO2-Y2O3 fluorites

The low Y/high Zr edge of the cubic defect fluorite solid solution in the system ZrO₂-TiO₂-Y₂O₃ in air is reassessed, as it is these compositions which have been suggested to offer the highest levels of mixed conductivity. Vegard's law is obeyed for values of x which lie within the cubic defect fluorite phase in Zr_1−x−yY_yTi_xO_2−δ for values of y=0.2 and 0.25. Measured lattice parameters show good agreement with those calculated from the Kim relation. Deviation from Vegard's law places the limit of the solid solution at x=0.18 and 0.20 for values of y=0.2 and 0.25, respectively, at 1500 °C. Discrepancies in current literature data can be shown to be due to differences in firing schedule such as slight temperature fluctuations and/or different cooling rates. A high level of care of sintering temperature and cooling profile is essential to form the most promising single-phase materials which contain maximum Ti-contents with low Y-contents. Contraction of the phase limit as a result of poor synthesis control leads to erroneously high values of bulk ionic conductivity while values of electronic conductivity are shown to be less affected.     

Structural and magnetic properties of the solid solution () YMn1−x(Cu3/4Mo1/4)xO3

Recently, the ferroelectromagnet YMnO₃ has been the focus of interest because it exhibits both antiferromagnetism (Néel temperature 80 K) and ferroelectricity (Curie temperature 914 K). There have been no reports of complete YMn_1−xM_xO₃ solid solutions in which substitution of the foreign M cation preserves the hexagonal P6₃cm structure. In contrast there exist several homeotypic phases with the general formula, Ln_1+nCu_nMO_3+3n (n=1 (M=Ti), 2 (M=V) and 3 (M=Mo); Ln: lanthanide). Several YMn_1−x(Cu_3/4Mo_1/4)_xO₃ compounds have been synthesized. The solid solution, from YMnO₃ (x=0) to YCu_3/4Mo_1/4O₃ (x=1) has been characterized by X-ray diffraction and transmission electron microscopy study. For 0<x<0.9, the compounds are found to crystallize in the non-centrosymmetric structure, space group P6₃cm, of YMnO₃. The Mn-free end member, x=1, crystallizes in a complex multiple cell, the superstructure being associated to Cu³⁺/Mo⁶⁺ cationic ordering. Dilution of the Mn³⁺ magnetic array by the paramagnetic (Cu²⁺) and diamagnetic (Mo⁶⁺) cations is found to decrease the antiferromagnetic ordering temperature and it becomes undetectable for x0.5 compositions.     

Phase equilibria in the pseudo-binary system SrO-Fe2O3

The phase relations in the pseudo-binary system SrO-Fe₂O₃ have been investigated in air up to 1150°C by means of powder X-ray diffraction and thermal analysis. Sr₃Fe₂O_7−δ, SrFeO_3−δ and SrFe₁₂O₁₉ are stable phases in the entire investigated temperature region, whereas Sr₂FeO_4−δ and Sr₄Fe₃O_10−δ decompose above 930±10°C and 850±25°C, respectively. Sr₄Fe₆O_13±δ is entropy-stabilized relative to SrFeO_3−δ and SrFe₁₂O₁₉ above 775±25°C. Extended solid-solution Sr_1±xFeO_3−δ was demonstrated. On the Fe-deficient side, the extent of solid solubility appeared to decrease gradually with temperature, whereas an abrupt decrease due to formation of Sr₄Fe₆O_13±δ was observed above 775°C on the Sr-deficient side.     

Au/CeO2/SiO2催化CO低温氧化反应过程中CeO2的作用（英文）

采用具有分等级孔道结构的SiO2(HMS)为载体,通过润湿浸渍引入少量CeO2,经焙烧得到CeO2/HMS复合载体,然后采用沉积沉淀法负载上Au纳米粒子,得到Au/CeO2/HMS三元复合催化剂.通过X射线衍射、程序升温还原和原位红外光谱等手段表征了催化剂的结构.结果表明,CeO2的存在可控制Au颗粒的沉积并稳定载体上的纳米Au颗粒.Au/CeO2/HMS上CO低温氧化反应完全转化温度为60oC.高度分散的Au0可以活化CO,CeO2颗粒则可以提供反应需要的氧.稳定性测试结果显示,反应48h催化剂活性维持不变.     

分步沉淀对CeO2-ZrO2-Y2O3-La2O3材料热稳定性的影响

研究了传统沉淀法和分步沉淀对CeO₂-ZrO₂-Y₂O₃-La₂O₃(CZ)材料结构和性能的影响. N₂-吸/脱附、 OSC、 H2-TPR和催化剂三效活性等测试结果表明:分步沉淀所制备的CZ材料表现出更优的氧化还原性能和织构性能.基于此,继续优化分步沉淀中晶种的含量(10%、 50%、 90%),结果表明:较少的晶种诱导可以极大程度提高材料热稳定性能和织构性能,但进一步增加晶种含量对材料热稳定性能提升作用不明显.其中,当晶种量为10%时,所得CZ材料在高温焙烧后仍保持最大比表面积及稳定的立方相结构,表现出最好的织构性能和热稳定性能,其负载的单Pd三效催化剂也因此表现出最优的三效催化活性.     

基于TiO2-Y2O3粉体催化发光甲醇气体传感器的研究

发现当甲醇气体通过TiO₂-Y₂O₃ (质量比为3∶1)粉体表面时, 可被空气中的O₂催化氧化产生强烈的化学发光, 基于此研制了一种新型的甲醇气体传感器. 此传感器对甲醇的检测具有较高灵敏度和较强的选择性. 在波长490 nm处进行定量分析, 催化发光强度与甲醇浓度在一定范围内呈良好的线性关系, 其线性范围为25.74～12870 mg/m³ (r＝0.9995, n＝8); 检出限为8.58 mg/m³(信噪比＝3). 外来物质如正己烷、三氯甲烷、苯、无水乙醇、甲醛、丙酮、氨、甲苯与甲醇共存时, 除了丙酮、乙醇和氨分别引起干扰外, 苯与其它气体不干扰测定. 该传感器工作时间可持续80 h以上, 是一种长寿命的、性能稳定的气体传感器, 并成功地实现了对甲醇气体的实时在线检测.     

La2O3对CuO/CeO2水煤气变换反应催化剂微观结构及催化性能的影响（英文）

以La2O3为助剂,采用共沉淀法制备了具有良好催化活性和热稳定性的CuO/CeO2-La2O3水煤气变换反应催化剂,其中,当La2O3含量为2wt%时,催化剂的催化性能最为优异.同时运用X射线衍射、N2吸附-脱附、Raman光谱、程序升温还原等手段,研究了不同含量的La2O3对CuO/CeO2催化剂微观结构及催化性能的影响.结果表明,La2O3助剂进入了载体CeO2的晶格并对CuO/CeO2催化剂的微观结构和催化性能产生了直接影响,适量La2O3的添加可以抑制CuO和CeO2晶格的长大、增强CuO与CeO2间的相互作用、提高催化剂的比表面积、促进CeO2载体中生成更多的氧空位,CuO/CeO2催化剂的催化活性和热稳定性也明显改善.     

Synthesis, crystal and band structures, and optical properties of a new lanthanide-alkaline earth tellurium(IV) oxide: La2Ba(Te3O8)(TeO3)2

A new quaternary lanthanide alkaline-earth tellurium(IV) oxide, La₂Ba(Te₃O₈)(TeO₃)₂, has been prepared by the solid-state reaction and structurally characterized. The compound crystallizes in monoclinic space group C2/c with a=19.119(3), b=5.9923(5), c=13.2970(19) Å, β=107.646(8)°, V=1451.7(3) Å³ and Z=4. La₂Ba(Te₃O₈)(TeO₃)₂ features a 3D network structure in which the cationic [La₂Ba(TeO₃)₂]⁴⁺ layers are cross-linked by Te₃O₈⁴⁻ anions. Both band structure calculation by the DFT method and optical diffuse reflectance spectrum measurements indicate that La₂Ba(Te₃O₈)(TeO₃)₂ is a wide band-gap semiconductor.     

Magnetic Co3O4 nanowires,preparation and properties

The Co₃O₄ nanowires have been successfully synthesized via modified template method.The as-prepared products have been characterized by EDS,TEM and HRTEM analysis.The magnetic behavior of it is investigated by a magnetic property measurement system.The nanowires exhibit some novel magnetic properties,which are different from its bulk material.The temperature dependence curves of magnetization in zero-field-cooling and field-cooling exhibit two peaks of antiferromagnetic at blocking temperature of～23 K and～31 K,respectively.The field dependent M（H） curves of the Co₃O₄ nanowires at T = 5 and 300 K both exhibit PM properties.Moreover,the diameter of nanowires is hence determined according to the finite size effect as approximately 7-11 nm,in consistent with the characterizations by HRTEM.     

Subsolidus phase equilibria and properties in the system Bi2O3:Mn2O3±x:Nb2O5

Subsolidus phase relations have been determined for the Bi-Mn-Nb-O system in air (750-900 °C). Phases containing Mn²⁺, Mn³⁺, and Mn⁴⁺ were all observed. Ternary compound formation was limited to pyrochlore (A₂B₂O₆O′), which formed a substantial solid solution region at Bi-deficient stoichiometries (relative to Bi₂(Mn,Nb)₂O₇) suggesting that ≈14-30% of the A-sites are occupied by Mn (likely Mn²⁺). X-ray powder diffraction data confirmed that all Bi-Mn-Nb-O pyrochlores form with structural displacements, as found for the analogous pyrochlores with Mn replaced by Zn, Fe, or Co. A structural refinement of the pyrochlore 0.4000:0.3000:0.3000 Bi₂O₃:Mn₂O_3±x:Nb₂O₅ using neutron powder diffraction data is reported with the A and O′ atoms displaced (0.36 and 0.33 Å, respectively) from ideal positions to 96g sites, and with Mn²⁺ on A-sites and Mn³⁺ on B-sites (Bi_1.6Mn²⁺_0.4(Mn³⁺_0.8Nb_1.2)O₇, (?227), a=10.478(1) Å); evidence of A or O′ vacancies was not found. The displacive disorder is crystallographically analogous to that reported for Bi_1.5Zn_0.92Nb_1.5O_6.92, which has a similar concentration of small B-type ions on the A-sites. EELS spectra for this pyrochlore were consistent with an Mn oxidation between 2+ and 3+. Bi-Mn-Nb-O pyrochlores exhibited overall paramagnetic behavior with negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. At 300 K and 1 MHz the relative dielectric permittivity of Bi_1.600Mn_1.200Nb_1.200O₇ was ≈128 with tan δ=0.05; however, at lower frequencies the sample was conductive which is consistent with the presence of mixed-valent Mn. Low-temperature dielectric relaxation such as that observed for Bi_1.5Zn_0.92Nb_1.5O_6.92 and other bismuth-based pyrochlores was not observed. Bi-Mn-Nb-O pyrochlores were readily obtained as single crystals and also as textured thin films using pulsed laser deposition.     

纳米管状结构立方萤石型CeO2的合成(英)

低温水热条件下，Ce⁴⁺离子经尿素水解均匀沉淀，在十八胺分子模板导向下形成了多层有序排列的纳米管状结构的立方萤石型CeO₂，采用粉末X射线衍射(PXRD)、透射电镜(TEM)、高分辨透射电镜(HRTEM)以及选区电子衍射(SEAD)等手段对产物进行了表征。结果表明，该结构是由单根外、内径分别为10～20 nm、5～6 nm左右的纳米管有序排列形成的纳米管束构成，且产物具有结晶性良好的立方萤石型CeO₂晶体结构。在管束的生长过程中，反应体系首先形成单根纳米管，继而管与管之间又相互缔合生长成多层有序排列的纳米管束。控制尿素的水解，获得了不同pH值下的反应产物，发现反应体系pH值在5～6之间时产物为立方萤石型CeO₂、6～8时为立方萤石型CeO₂与六方型Ce(OH)CO₃的混合物、大于8则为六方型Ce(OH)CO₃。     

Synthesis, band structure, and optical properties of Ba2ZnV2O8

A novel compound Ba₂ZnV₂O₈ has been synthesized in high temperature solution reaction and its crystal structure has been characterized by means of single crystal X-ray diffraction analysis. It crystallizes in monoclinic system and belongs to space group P2₁/c with a=7.9050(16), b=16.149(3), , β=90.49(3). It builds up from 1-D branchy chains of [ZnV₂O₈⁴⁻]_∞, and the Ba²⁺ cations are located in the space among these chains. The IR spectrum, ultraviolet-visible diffuse reflection integral spectrum and fluorescent spectra of this compound have been investigated. The calculated results of energy band structure by the density functional theory method show that the solid-state compound of Ba₂ZnV₂O₈ is an insulator with direct band gap of 3.48 eV. The calculated total and partial density of states indicate that the top valence bands are contributions from the mixings of O-2p, V-3d, and Zn-3d states and low conduction bands mostly originate from unoccupied antibonding states between the V-3d and O-2p states. The V-O bonds are mostly covalence characters and Zn-O bonds are mostly ionic interactions, and the ionic interaction strength is stronger between the Ba-O than between the Zn-O. The refractive index of n_x, n_y, and n_z is estimated to be 1.7453, 1.7469, and 1.7126, respectively, at wavelength of 1060 nm for Ba₂ZnV₂O₈ crystal.     

Synthesis and luminescent properties of rare-earth-doped CeO2–CaF2 solid solutions via chemical solution routes

CeO₂–CaF₂ solid solutions were synthesized by a chemical solution method starting from metal acetates, trifluoroacetic acid as a fluorine source, and anhydrous ethanol as a solvent. Precursor gels, which were obtained by drying the resultant ethanolic solution at 110 °C, were heat-treated at a temperature in the range 400–1000 °C in air to obtain powdery products. Elemental analysis by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed that heating products actually contained cerium, calcium, oxygen, and fluorine. According to X-ray diffraction analysis, possible reaction pathways under high-temperature treatments were considered as initial formation of fluorides (CeF₃ and CaF₂), subsequent oxidation of Ce³⁺ to Ce⁴⁺ in air, and final conversion to fluorite-type Ce–Ca–O–F solid solutions. Doping of Eu³⁺ or Sm³⁺ ions in the solid solutions led to occurrence of their characteristic photoluminescence due to intra-configurational f–f electronic transitions. Photo-excitation was achieved by irradiation with near ultraviolet light mainly through charge transfer from O²⁻ to Ce⁴⁺ in the solid solutions and subsequent energy transfer to the doped ions. Spectral structures of photoluminescence suggested the occupation of Eu³⁺ or Sm³⁺ in Ce⁴⁺ sites with inversion symmetry in the solid solutions.     

Polymorphism in the Sc2Si2O7-Y2Si2O7 system

This paper examines the structural changes with temperature and composition in the Sc₂Si₂O₇-Y₂Si₂O₇ system; members of this system are expected to form in the intergranular region of Si₃N₄ and SiC structural ceramics when sintered with the aid of Y₂O₃ and Sc₂O₃ mixtures. A set of different compositions have been synthesized using the sol-gel method to obtain a xerogel, which has been calcined at temperatures between 1300 and 1750 °C during different times. The temperature-composition diagram of the system, obtained from powder XRD data, is dominated by the β-RE₂Si₂O₇ polymorph, with γ-RE₂Si₂O₇ and δ-RE₂Si₂O₇ showing very reduced stability fields. Isotherms at 1300 and 1600 °C have been analysed in detail to evaluate the solid solubility of the components. Although, the XRD data show a complete solid solubility of β-Sc₂Si₂O₇ in β-Y₂Si₂O₇ at 1300 °C, the ²⁹Si MAS-NMR spectra indicate a local structural change at x ca. 1.15 (Sc_2−xY_xSi₂O₇) related to the configuration of the Si tetrahedron, which does not affect the long-range order of the β-RE₂Si₂O₇ structure. Finally, it is interesting to note that, although Sc₂Si₂O₇ shows a unique stable polymorph (β), Sc³⁺ is able to replace Y³⁺ in γ-Y₂Si₂O₇ in the compositional range 1.86?x?2 (where x is Sc_2−xY_xSi₂O₇) as well as in δ-Y₂Si₂O₇ for compositions much closer to the pure Y₂Si₂O₇.     

On the solid solution of the spinel phase in the system NiO-Al2O3

The solid solubility of Al₂O₃ in NiAl₂O₄ spinel has been investigated by powder X-ray diffraction of samples prepared by solid state synthesis. The solid solution region found was in agreement with a previous report. The cubic cell parameter of the spinel solid solution was observed to decrease with increasing alumina content. Spinel with high alumina content was shown to be close to an inverse spinel as previously reported for stoichiometric NiAl₂O₄ and the inversion parameter proved to be relatively independent of the overall composition.     

Interaction in the Ga2S3-Y2O2S system

The phase diagram of the Ga₂S₃-Y₂O₂S system has been investigated by differential thermal, X-ray powder diffraction, microstructural, and thermodynamic analyses. It has been established that the system is eutectic, and solubility at 295 K from the Ga₂S₃ side reaches 3 mol % Y₂O₂S. The coordinates of the eutectic point are 14 mol % Y₂O₂S and 1320 K.