The stability of nanosized HZSM-5 zeolite: a high-resolution solid-state NMR study

The thermal and hydrothermal stabilities of HZSM-5 zeolites with crystal sizes less than 100 nm have been studied by multinuclear solid-state NMR, combined with BET and XRD. As evidenced by Al-27 and Si-29 MAS as well as their corresponding cross-polarization/MAS NMR investigations, the thermal stability of nanosized HZSM-5 is not so good as that of microsized HZSM-5. This is due to two processes concerning dealumination and desilicification involved in the calcination of nanosized HZSM-5, while only the dealumination process is conducted in microsized HZSM-5 under the similar calcination process. The hydrothermal stability of nanosized HZSM-5 is, contrary to what was expected, not so bad as that of the microsized HZSM-5 in the course of steam treatment. The actual resistance of the hydrothermal stability to the crystal size of HZSM-5 can be ascribed to an active reconstruction of zeolitic framework through an effective filling of amorphous Si species into nanosized HZSM-5 during hydrothermal treatment. (C) 2001 Published by Elsevier Science B.V.

Structural and optical properties of YAG : Ce3+ phosphors by sol-gel combustion method

High-quality Ce3+-doped Y3Al5O12 (YAG:Ce3+) phosphors were synthesized by a facile sol-gel combustion method. In this sol-gel combustion process, citric acid acts as a fuel for combustion, traps the constituent cations and reduces the diffusion length of the precursors. The XRD and FT-IR results show that YAG phase can form through sintering at 900 degrees C for 2 h. This temperature is much lower than that required to synthesize YAG phase via the solid-state reaction method. There were no intermediate phases such as YAlO3 (YAP) and Y4Al2O9 (YAM) observed in the sintering process. The average grain size of the phosphors sintered at 900-1100 degrees C is about 40 nm. With the increasing of sintering temperature, the emission intensity increases due to the improved crystalline and homogeneous distribution of Ce3+ ions. A blue shift has been observed in the Ce3+ emission spectrum of YAG:Ce3+ phosphors with increasing sintering temperatures from 900 to 1200 degrees C. It can be explained that the decrease of lattice constant affects the crystal field around Ce3+ ions. The emission intensity of 0.06Ce-doped YAG phosphors is much higher than that of the 0.04Ce and 0.02Ce ones. The red-shift at higher Ce3+ concentrations may be Ce-Ce interactions or variations in the unit cell parameters between YAG:Ce3+ and YAG. It can be concluded that the sol-gel combustion synthesis method provides a good distribution of Ce3+ activators at the molecular level in YAG matrix. (c) 2005 Elsevier B.V. All rights reserved.

Sol-gel combustion synthesis and luminescence Of Y4Al2O9 : Eu3+ nanocrystal

Y4Al2O9:EU3+ phosphor was synthesized through a sol-gel combustion method. The Y4Al2O9 phase can form through sintering at 800 degrees C. This temperature is much lower than that required via the solid state reaction method. The average grain size of the phosphor was about 30 run. Compared with the amorphous phosphor, the charge transfer band of crystalline phosphor shows a blue shift. The emission Of Y4Al2O9:Eu3+ indicates the existence of two luminescent centers, in agreement with the crystal structure of Y4Al2O9. Higher doping concentration could be realized in Y4Al2O9 nanocrystal host lattice. This indicates that the sol-gel combustion synthesis method can increase emission intensity and quenching concentration due to a good distribution of EU3+ activators in Y4Al2O9 host. (c) 2005 Elsevier B.V. All rights reserved.

晶格匹配氮化镓和氧化锌基外延薄膜衬底材料ScAlMgO4晶体生长研究

采用提拉法成功生长了氮化镓和氧化锌基外延薄膜晶格匹配的ScAlMgO4单晶衬底材料,晶体呈透明白色,尺寸为Ф30mm×59mm,表面部分沿解理面有裂纹.粉末X射线衍射（XRD）分析表明经1400℃固相反应烧结的原料基本合成了ScAlMgO4多晶相.初步的偏光显微镜观察、晶体的粉末XRD表征、透过光谱和双晶摇摆测试表明晶体具有较好的光学性质和结晶质量.研究表明晶体本身的层状结构、较大的温度梯度和热应力的不均匀性是生长过程中引起晶体开裂的几个主要原因.

Enhancement of ferromagnetic properties in In1.99Co0.01O3 by additional Cu doping

This paper reports room-temperature ferromagnetism in Co- and Cu-doped In2O3 samples synthesized by a solid-state reaction method. Structure and composition analyses revealed that Co and Cu were incorporated into the In2O3 lattices. Photoluminescence measurement revealed an additional emission at 520 urn from these doped samples. The magnetic measurement showed that additional Cu doping greatly enhanced the ferromagnetism of In1.99Co0.01O3 bulk samples. The implication of the effects of additional Cu doping is also discussed. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Yb:Y2O2S的粉体制备和光谱性质

通过助熔剂固相反应法制备了5%Yb掺杂的硫氧化钇(Y2O2S)粉体。通过对其漫反射光谱和荧光光谱的测量，估算得Yb3+离子在Y2O2S晶格中的晶场分裂。由光谱数据计算得Yb3+离子的2F7/2能级在Y2O2S中的分裂值为709cm-1，适合于Yb3+离子的准三能级的激光运转。由5％Yb：Y2O2S的发射光谱拟合得出其峰位，峰高及峰宽。为了比较，相关的5％Yb：YAG的数据也被给出。

Dielectric relaxation and giant dielectric constant of Nb-doped CaCu3Ti4O12 ceramics under dc bias voltage

CaCu3Ti(4-x)Nb(x)O(12) (x = 0, 0.01, 0.08, 0.2) ceramics were fabricated by a conventional solid-state reaction method. The ceramics showed the body-centered cubic structure without any foreign phases and the grain size decreases with Nb doping. Two Debye-type relaxations were observed for the Nb-doped samples at low frequency and high frequency, respectively. The complex electric modulus analysis revealed that the surface layer, grains and grain boundaries contributed to the dielectric constant. The low-frequency dielectric constant relative to the surface layer decreased to a minimum and then increased with the dc bias voltage at 100 Hz, which were well explained in terms of a model containing two metal oxide semiconductors in series, confirming the surface layer in the ceramics. The shift voltage V-B corresponding to the minimal capacitance increased with increase of the composition x. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of fabrication conditions on I-V properties for ZnO varistor with high concentration additives by sol-gel technique

Polycrystalline nano-grain-boundary multi-doping ZnO-based nonlinear varistors with higher concentration additives have been fabricated by sol-gel and standard solid-state reaction method, of which the best sample has a very high threshold voltage of E-b = 3300 V/mm. The effect of sintering processes, sintering temperature and sintering time, and that of additive concentration of Bi2O3 on E-b of the samples are systematically investigated. The results show that the great merit of sol-gel method is its high threshold voltage obtained by a lower sintering temperature than the solid-state reaction method. The present work also shows that five phases including solid-state sintering, rich Bi liquid phase formation and ZnO as well as other additive dissolution, ZnO grain growth, the secondary phase sufficient formation and evolution have been experienced at different sintering temperatures. The hole type defect and nonhomogeneity of the microstructure will lead to the decrease of threshold voltage, i.e., the grain size and the homogeneity of the material will be important factors and directly affect the characteristic of the varistor. The sintering characteristic and the influence of Bi2O3 content on the threshold voltage are also discussed. (c) 2004 Elsevier B.V. All rights reserved.

Effects of doping lanthanide ions in YAG : Ce system on the spectral properties of Ce3+

(Y0.95Ln(0.01)Ce(0.04))(3)Al5O12 phosphors were synthesized by high-temperature solid state reaction under reducing atmosphere and the doping effects of lanthanide ions (Ln(3+)) on the luminescence properties of phosphors were studied. YAG: Ce, Ln spectra of excitation and emission show that the influence between Ce3+ and Ln(3+) can be divided into the following three types

Rectangular AgIn(WO4)(2) nanotubes: A promising photoelectric material

Rectangular AgIn(WO4)(2) nanotubes with a diameter range of 80 to 120 nm and length up to 2 mu m have been synthesized by a hydrothermal method. These nanotubes exhibit interesting white light emissions when using 320 nm as the excitation wavelength. A photocatalytic reaction for water decomposition to evolve K, was performed under UV irradiation, and the rate of H, evolution is nearly seven times that of the sample prepared by a solid-state reaction, which shows much higher photocatalytic activities compared with their bulk counterparts.