材料期刊网

Effects of Nitridation Temperature on Characteristics of Gallium Nitride Thin Films Prepared Via Two-Step Method

Chee Yong Fong , Sha Shiong Ng , Fong Kwong Yam , Haslan Abu Hassan , Zainuriah Hassan

金属学报 doi:10.1007/s40195-015-0206-z

关键词:

Theoretical Prediction of Elastic Stiffness and Minimum Lattice Thermal Conductivity of Y3Al5O12, YAlO3 and Y4Al2O9

Journal of the American Ceramic Society

Combining Clarke's model with first-principles calculation of average sound velocity, the minimum lattice thermal conductivities (kappa(min)) of Y3Al5O12 (YAG), YAlO3 (YAP) and Y4Al2O9 (YAM) are predicted to be 1.59, 1.61, and 1.10 W.(m.K)(-1), respectively. The weak Y-O polyhedra provide "weak zones" that scattering phonons and lead to the low kappa(min) of ternary Y-Al-O compounds. In addition, the extremely low kappa(min) of YAM is attributed to its higher levels of local disorder of crystal structure and weaker chemical bonding compared with those of YAG and YAP. Inspired by theoretical predictions, dense and phase-pure YAM is synthesized and the experimental thermal conductivity is only 1.56 W.(m.K)(-1) at 1273 K. Finally, YAM is highlighted as a potential thermal barrier material for its low thermal conductivities at temperatures from 473 to 1273 K.

关键词: barrier coatings;single-crystal;gas;stability

Adsorption of hydrogen on porous materials of activated carbon and zeolite NaX crossover critical temperature

Journal of Supercritical Fluids

Hydrogen adsorption properties of typical porous materials, activated carbon and zeolite NaX, are studied through isotherm measurements at pressure up to 7 MPa crossover the critical temperature. The Soave-Redlich-Kwong equation of state is selected for calculation of compressibility factor of hydrogen. The two adsorbents exhibit remarkably different hydrogen uptake capacities. which are attributed to their framework structures and porous surfaces. At near critical temperatures, significant drops and recoveries of excess adsorption are observed on the isotherms. The multilayer adsorption and associated reduced density and increased volume of the adsorbed phase are derived from the extents of adsorption drops. The recovery is attributed to the bias of compressibility factor from the assumed equation of state. The negative adsorption is observed at subcritical temperature, and explained by the conception of pore critical temperature and relevant calculation. The isosteric heats of adsorption are determined as 2.1 kJ/mol for activated carbon and 4.4 kJ/mol for NaX, respectively.

关键词: Hydrogen adsorption isotherm;Activated carbon;Zeolite Nax;Critical;temperature;Compressibility factor;high-pressure adsorption;supercritical hydrogen;neutron-diffraction;confined phases;critical-point;storage;physisorption;isotherms;capacity;behavior

OCDMA素数码相关值分布的研究

周海贤 , 许国良 , 姚伟

量子电子学报 doi:10.3969/j.issn.1007-5461.2008.04.020

在OCDMA系统中,系统地址码的相关值是直接影响码字性能的关键参数.对地址码相关值分布的研究是一项重要的工作.通过严密的代数运算以及统计分析,对Kwong所提出的PC相关值分布公式进行了一项小的修正.通过同样的方法,并根据逐步分析和简单的数据预测,得到了新的关于EQC的相关值分布公式.基于该EQC相关值分布公式,计算并比较了不同码字组合情况下所对应的误码率,最后得出采用EQC非零码字可以有效提高码字性能.

关键词: 光通信 , 相关值分布 , 概率 , 误码率

诱惑态下相位差分量子密钥分发效率分析

赵峰

量子电子学报 doi:10.3969/j.issn.1007-5461.2009.04.010

讨论基于微弱相干脉冲的相位差分量子密钥分发系统,综合分析系统的安全性问题,给出了密钥生成效率表达式.分析诱惑态对相位差分量子密钥分发系统安全性的影响,并给出了结合诱惑态后的密钥生成效率表达式.分析结果表明,结合诱惑态的相位差分量子密钥分发过程不再受到分光子攻击和序列攻击的威胁,其密钥分发效率与Hoi-Kwong等提出的诱惑态的表述结果一致.实验数据显示,结合诱惑态后的相位差分系统.其安全传输距离得到了进一步提高,量子密钥分发效率提高了约1个数量级.

关键词: 量子光学 , 相位差分 , 诱惑态 , 密钥生成效率

掺钕钇铝石榴石陶瓷的制备与性能

张旭东 , 刘宏 , 王继扬 , 何文 , 徐国纲

人工晶体学报 doi:10.3969/j.issn.1000-985X.2004.03.003

以Al2O3、Y2O3、Nd2P3为起始原料,用固相合成方法在1500℃、2h条件下合成了掺钕钇铝石榴石(1.1at.%Nd:YAG)粉料.研究表明,在固相反应过程中,首先形成中间相Y4Al2O9(YAM)、YAlO3(YAP)而最终形成单相Y3Al5O12(YAG).将上述粉料经等静压成型并在低真空状态下于1750℃烧结3h,获得呈半透明状态的Nd:YAG陶瓷,其相对密度达到98.68%,显微结构均匀,荧光性能与0.9at% Nd:YAG单晶材料相近.

关键词: 钇铝石榴石 , 固相反应 , 激光陶瓷 , 荧光性能

固相反应合成Nd:YAG及其性能表征

张旭东 , 徐国纲 , 王继扬 , 刘宏

稀有金属材料与工程

采用纳米级超细Al2O3和Y2O3粉料,通过固相反应合成Nd:YAG.由于反应物颗粒细,反应活性和组分均匀性高以及Y3+、Al3+离子间相互扩散,在1 100℃的低温条件下可同时形成YAM、YAP和YAG相;在1 400℃下保温2 h～3h可合成性能良好的单相Nd:YAG粉料,其颗粒尺寸达到100nm左右.其合成温度降低150℃～200℃.

关键词: 固相反应 , 钇铝石榴石 , 性能 , 合成粉体

Synthesis of YAG powder by the modified sol-gel combustion method

Journal of Alloys and Compounds

Yttrium aluminum garnet (YAG) precursor was prepared by sol-gel combustion method using ethanol as solvent. Nano-sized YAG powders were obtained by precalcining the precursor at 500 degrees C, and then calcining at different temperatures. The phase formation and characteristics of YAG powders were investigated by means of XRD, TG/DSC and TEM. Pure crystalline YAG phase was obtained at 800 degrees C, without any intermediate phases such as YAlO(3) (YAP) and Y(4)Al(2)O(9) (YAM). Moreover, it was found that the elliptical YAG powder calcined at 900 degrees C for 2 h was well-crystallized with an average size of 30 nm, and had a good dispersity. (C) 2009 Elsevier B.V. All rights reserved.

关键词: Nanostructured materials;Sol-gel processes;X-ray diffraction;Thermal;analysis;yttrium-aluminum-garnet;luminescence properties;ceramics;phosphor;laser;nanoparticles;performance;fabrication;precursors;water

共沉淀法YAG、Nd:YAG纳米粉体的制备、结构与光谱性能研究

苏静 , 张庆礼 , 谷长江 , 孙敦陆 , 邵淑芳 , 殷绍唐

功能材料

采用共沉淀方法,以氨水为沉淀剂,与硝酸盐的混合溶液反应得到YAG、Nd:YAG前驱体,并在不同的温度下对前驱体进行锻烧.利用红外光谱(FT-IR)、热重/差热分析(TG/DTA)、X射线衍射(XRD)、透射电镜(TEM)等技术对YAG前驱物及煅烧粉体进行表征,对Nd:YAG粉体的发光性能进行了测试.结果表明,在800℃下煅烧YAG前驱体,得到纯YAG晶相,无YAP、YAM中间相的出现;XRD、TEM和比表面分析表明在800～1000℃煅烧所得粉体晶粒直径为40～100nm,具有较好的分散性.同时荧光测试表明Nd:YAG粉体具有良好的发光性能.

关键词: YAG , 共沉淀法 , 纳米粉体 , 发光

高能球磨Al-Y₂O₃粉体固相反应制备YAG陶瓷的研究

李长青 , 张明福 , 左洪波 , 韩杰才 , 孟松鹤

无机材料学报 doi:10.3724/SP.J.1077.2008.01131

用高纯Al粉体和Y₂O₃粉体(Al-Y₂O₃粉体)为原料采用固相反应法制备了YAG陶瓷. Al-Y₂O₃粉体高能经过球磨, 煅烧生成YAG粉体, 再真空烧结制备高致密YAG陶瓷. 采用DTA-TG对球磨Al-Y₂O₃粉体进行分析, 采用XRD、SEM对球磨的Al-Y₂O₃粉体、YAG粉体及YAG陶瓷进行了表征. 实验表明: Al-Y₂O₃粉体在～569℃时, Al粉强烈氧化, 并与Y₂O₃粉反应, 600℃煅烧出现YAM相, 随煅烧温度升高出现YAP相, 1200℃煅烧生成YAG粉体. 成型YAG素坯在1750℃保温2h真空烧结出YAG相陶瓷, YAG陶瓷相对密度可达98.6%, 晶粒生长均匀, 晶粒尺寸为810μm.

关键词: 高能球磨 , Al , Y₂O₃ , DTA-TG , YAG