A new high efficiency green luminescent material - the system Al2O3-B2O3 containing Ce3+ and Tb3+ ions

To obtain high efficiency luminescent materials, the system Al2O3-B2O3 containing Ce3+ and Tb3+ ions with variation of B2O3-content, has been prepared by Al2O3, H3BO3, CeO2 and Tb4O7 under reducing atmosphere at 1250(j)ae. It is notable that the brightness of the sample with appropriate composition is similar to that of commercial phosphorous containing Ce3+ and Tb3+, indicating that a new high efficency green luminescent material was obtained with appropriate B2O3-content.

Investigation of Pr valence and relationship between bond covalency and T-c in Y1-xPrxBa2Cu3O7 (x = 0-1)

The valence of Pr and relationship between bond covalency and T-c in Y1-xPrxBa2Cu3O7 (x = 0-1) have been studied using complex chemical bond theory. The results indicate that the depression of superconductivity in Y1-xPrxBa2Cu3O7 can be reasonably explained by bond covalency difference for the bonds between CuO2 plane and CuO chain. T-c decreases with the decreasing of bond covalency difference and reaches zero when bond covalency difference is zero (or bond covalency in CuO2 exceeds that in CuO chain) at Pr concentration 0.55 and valence +3.30. These are in good agreement with the experiments and meanwhile suggest that the valence of Pr is + 3.30 in Y1-xPrxBa2Cu3O7. The results also indicate that for Pr valence less than +3.15, superconductivity always exists for whatever Pr concentration, whereas for Pr with a valence of +4.0, superconductivity disappears as soon as Pr concentration exceeds 0.19. This supports with the viewpoint that higher valence Pr will contribute more electrons to CuO2 plane, filling the mobile holes responsible for conduction. For PrBa2Cu3O7 with no Ba-site Pr, our calculation suggests that it will be a superconductor if the average valence of Pr is less than +3.15. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

Pt/Al_2O_3和Pt/CeO_2/Al_2O_3催化甲烷部分氧化制合成气反应

研究了Ｐｔ／Ａｌ２Ｏ３和Ｐｔ／ＣｅＯ２／Ａｌ２Ｏ３对甲烷部分氧化制合成气反应的催化活性，发现Ｐｔ／ＣｅＯ２／Ａｌ２Ｏ３显示了更高的甲烷转化率和合成气选择性．用Ｈ２－ＴＰＲ、Ｈ２－ＴＰＤ、ＳＥＭ－ＥＤＸ和ＸＲＤ等技术对催化剂进行了表征．ＣｅＯ２和Ｐｔ相互作用促进Ｐｔ在催化剂表面的分散，抑制Ｐｔ在催化剂表面的迁移；降低了催化剂的燃烧活性，提高了催化剂的部分氧化活性和选择性，可避免因催化剂床层局部温度过高而导致催化剂活性下降或失活，提高了催化剂的稳定性．同时，ＣｅＯ２通过促进水汽变换反应使反应体系迅速达到平衡，提高了催化剂对Ｈ２的选择性.

Synthesis, extraction and electronic structure of Ce@C-2n

In view of the growing interest in endohedral lanthanide fullerenes, Ce, as a typical +4 oxidation state lanthanide element, has been systematically studied. The synthesis, extraction and electronic structure of Ce@C-2n are investigated. Soot containing Ce@C-2n was synthesized in high yield by carbonizing CeO2-containing graphite rods and are back-burning the CeC2-enriched cathode deposit in a DC are plasma apparatus. Ce@C-2n, dominated by Ce@C-82, can be efficiently extracted from the insoluble part of the soot after toluene Soxhlet extraction by pyridine at high temperature and high pressure in a closed vessel. About 60% Ce@C-2n (2n = 82,80,78,76) and 35% Ce@C-82 can be enriched in the pyridine extract. This fact is identified by desorption electron impact mass spectrometry (DEI MS). The electronic structure of Ce@C-2n is analyzed by using X-ray photoemission spectroscopy (XPS) of pyridine-free film. It is suggested that the encapsulated Ce atom is in a charge state close to +3 and was effectively protected from reaction with water and oxygen by the enclosing fullerene cage. Unlike theoretical expectation, the electronic state of Ce@C-82 is formally described as Ce+3@C-82(3-). (C) 1997 Elsevier Science Ltd.

Synthesis and properties of cerium oxide nanometer powders by pyrolysis of amorphous citrate

CeO2 nanometer powders of different sizes were prepared at low temperature by pyrolysis of amorphous citrate. XRD patterns show that CeO2 is cubic in structure, space group O-h(5)-F-M3M. TEM indicates that the prepared CeO2 is spherical in shape, and the particle size distribution is in narrow range. It was found that calcination temperature is a more important factor affecting the crystallite size of CeO2 than calcining time, the smaller the particle, the bigger the crystal lattice distortion, the worse the crystal growth. Solubility test of CeO2 in nitric acid reveals that the surface activity of CeO2 decreases with the increasing particle sizes. IR spectra analysis shows that the absorption of Ce-O bond is shifted to higher energy with the decrease of CeO2 particle sizes.

PREPARATION AND PROPERTIES OF BACUO2.5 AND ITS RELATED OXIDES

The compound BaCuO2.5 Was obtained using BaO2 and CuO as starting materials, and its various properties were investigated. It belongs to the orthorhombic system with a = 8.55 angstrom, b = 10.56 angstrom, and c = 7.62 angstrom. The p-type semiconductor Ba

水合二高碘酸氢合铜(Ⅲ)酸钾钠配合物的合成、结构与光谱性质

本文报道了碱溶液中获得组份为Na_4K[Cu(HIO_6)_2]·12H_2O晶体配合物.用X-射线衍射法测定了晶体结构.晶体属单斜晶系,P2_1/c空间群,a=6.108(2)(?),b=25.055(10)(?),c=14.716(7)(?),β=97.77(3)°,V=2231(2)(?)~3,D_c=2.555g/cm~3,Z=4.晶体中二个畸变的IO_5(OH)八面体与中心铜原子螯合,构成CuO_4平面;Cu—O平均键长为1.83(?);加上CuO_4平面上侧与铜原子形成弱配位的氧原子;共有五个氧原子与铜原子构成近似为C_(2v)点群对称的四方单锥多面体.在碱性水溶液中,配合物的紫外吸收峰的衰减表明,[Cu(HIO_6)_2]~(5-)还原为一级反应.

CYCLIC VOLTAMMETRIC AND SPECTROELECTROCHEMICAL STUDIES OF COPPER IN ALKALINE-SOLUTION

The behaviour of the electroplated copper film electrode on tin oxide/glass or glassy carbon surface was studied in potassium hydroxide medium by cyclic voltammetry and in situ transmission spectroelectrochemistry. The results indicate that the electroplated copper film electrode is similar to a copper electrode and cyclic voltammetry with this electrode affords more resolution. The anodic peaks were found to correspond successively to the adsorption of oxygen, the formation of a surface layer of Cu2O, the formation of a surface layer of Cu(OH)2 or CuO and formation of a thick multilayer film of CuO. This is the first time it has been proposed that a surface layer of Cu(OH)2 or CuO is formed from the oxidation of the surface layer of Cu2O. Similarly, a clear interpretation is presented that the cathodic peaks correspond successively to the reduction of CuO to Cu2O, the reductions of Cu2O to Cu and the soluble Cu(II) species to Cu. On the other hand, a shoulder peak related to the chemical transformation of Cu(OH)2 to CuO was first observed.

Vb族元素掺杂对YBa_2 Cu_3 O_(7-y)载流子浓度的影响

众所周知,在YBa_2Cu_3O_(7-y)中Cu_1-O链起着稳定晶体结构和向体系提供载流子的作用,而Cu_(2-)O面则影响超导电子的运动。因此,利用Vb族元素可以提供更多的自由电子的特点来进行掺杂对研究YBa_2Cu_3O_(7-y)超导体中超导电子的运动和Cu—O链、Cu—O面的作用是很有意义的。

水合二高碲酸合铜(Ⅲ)酸氢四钠配合物的合成、结构和紫外吸收光谱

在碱性水溶液中获得了组分为Na_4H[Cu(H_2TeO_6)_2]·17H_2O的晶体配合物。用X-射线衍射法测定了单晶结构,晶体属三斜晶系,空间群 P_1,a=0.5939(2)nm,b=0.8957(3)nm,c=1.2555(3)nm,α=98.49(2)°,β=98.98(2)°,γ=93.94(2)°,V=0.6495(3)nm~3,M=913.7,Dc=2.34s/cm~3,Z=1.晶体中二个畸变的TeO_4(OH)_2八面体与中心Cu(Ⅲ)离子螯合,构成属准D_(2h)点群对称的CuO_4平面,Cu—O键长分别为0.1830nm和0.1844nm。 配合物溶液的紫外吸收光谱,于270nm和405nm处有两个强的配体至金属电荷转移谱带。

Bi系中2212相的超导电性研究

已知在Bi系高Tc超导体中存在三个超导相:2223相的Tc～110k,c～37(?);2212相的Tc～85k,c～30.6(?);2201相的Tc～10k。在实验过程中,我们注意到还可能有另外的超导相存在,通过改变元素名义配比和制备工艺观察到一个具有2212相结构,但Tc却表现为～105k的新现象存在。 实验部分 样品制备采用固相反应方法将Bi_2O_3、PbO、Sb_2O_3、SrCO_3、CaCO_3、CuO(均为A.R.级)混匀、碾磨,于～810℃在刚玉坩埚中预烧20h;再碾,压片后于～870℃在磁舟中烧结60-240h,然后作测试分析。

THE CATALYTIC BEHAVIOR AND REACTION-MECHANISM OF THE BI-CE-O SYSTEM CATALYSTS IN THE OXIDATIVE DEHYDROAROMATIZATION OF PROPYLENE

Oxidative dehydroaromatization of propylene was investigated by the pulse technique over two kinds of single oxide catalysts. With the Bi2O3 catalyst, the main dimer product was 1,5-hexadiene, and the dimerization activity was stable to pulse number even if the catalyst was partly reduced to the bulk. With the CeO2 catalyst, benzene was mainly formed instead of 1,5-hexadiene, but the activity decreased rapidly with increasing pulse number, indicating that only the lattice oxygen near the catalyst surface could be used for oxidative dimerization and the further aromatization. The Bi-Ce-O system catalyst was found in this study to give higher aromatization activity and showed better stability, compared to the Bi-Sn-O catalyst. Although the Bi-Ce-O catalyst was only a mixture of the two component oxides from X-ray diffraction analysis, there was a significant combination effect on the selectivity to benzene. The highest and the most stable selectivity of benzene was obtained at Bi/Ce = 1. In the TPD spectrum of Bi-Ce-O catalyst, there are not only the lattice oxygen (beta-oxygen) over 620-degrees-C due to the reduction of Bi2O3, but also a great deal of the alpha-oxygen desorbed about 400-degrees-C, which is considered the absorbed oxygen in the bulk. This absorbed oxygen could probably be a compensation of the lattice oxygen through the route of gaseous --> absorbed --> lattice oxygen in the binary catalyst system. By the kinetic study on the Bi-Ce-O catalyst, the dimer formation rate was the first-order with respect to the partial pressure of propylene and zero-order of oxygen. Although detail investigation would be made further, it was considered that the complete oxidation of propylene would mainly take place parallelly on some different sites, and the rate-determining step of propylene dimerization occurred probably between an adosrbed propylene and a gaseous one by an Eley-Rideal type mechanism.

一个新的CuxSbOy化合物的合成

在研究Bi系超导样品中各组分间的相图关系时,我们发现了一个新的Cu_xSbO_y化合物。关于Cu—Sb—O体系只有CuSb_2O_5化合物已见报导1 实验部分试样制备采用固相反应方法,将Sb_2O_3,CuO(A,R级)混匀、碾磨,于900℃在刚玉坩锅中灼烧24小时。X—ray衍射分析在日本D/max—Ⅱв衍射仪上进行

高Jc Ag-Bi-Pb-Sr-Ca-Cu-O超导材料

Bi_2Sr_2Ca_2Cu_3O_y-Ag_x、Bi_(1.7)Pb_(0.3)Sr_2Ca_2Cu_3O_y-Ag_x和Bi_(1.7)Pb_(0.3)Sr_2Ca_2Cu_(3.2)O_y-Ag_x系列的超导材料是用固相反应的方法合成的。原料为分析纯AgNO_3、PbO、Bi_2O_3、CaCO_3、SrCO~3和CuO。把试剂按所需配比混和研磨后,在800℃烧12h,研磨压片,片子在850℃烧结200h,破碎、研磨后,按配比加入AgNO_3·800℃灼烧12h,再次研磨、压片,850℃再烧结200h,炉冷至室温。

BiPbSbSrCaCuO的超导电性

据报,在BiPbSrCaCuO中加Sb形成BiPbSbSrCaCuO体系的T_c可达130K。但其组成、结构、性质等均未见详细报道。我们合成了一系列BiPbSbSrCaCuO,发现了一个具有2212相结构、但T_c却为～110K的超导相。 试样制备包括将Bi_2O_3,PbO,Sb_2O_3,SrCO_3,CaO和CuO(AR级)混匀、碾磨、于