Bi，Sb合金化对AZ91镁合金组织、性能影响机理研究

利用大角重位点阵模型建立了AZ91镁合金α相［0001］对称倾斜晶界原子结构模型，应用实空间的连分数方法计算了Mg合金的总结构能，合金元素引起的环境敏感镶嵌能及原子间相互作用能，讨论了主要合金元素Al及Bi，Sb在AZ91中的合金化行为.计算结果表明，Al，Bi，Sb固溶于α相内或晶界区使总结构能都降低，起到固溶强化作用；合金元素在AZ91α相内趋于均匀分布，在晶界区易占位于三角椎上部.AZ91镁合金中加入Bi或Sb时，Bi或Sb比Al容易偏聚于晶界，从而抑制了Al在晶界的偏聚，促进基体中连续的Mg₁₇Al₁₂相的析出，提高AZ91合金室温性能； AZ91合金中(α相内和晶界区)主要合金元素Al和微加元素Bi，Sb都能够形成有序相Mg₁₇Al₁₂，Mg₃Bi₂或Mg₃Sb₂，且在晶界区形成的量大.Bi，Sb加入AZ91合金中，由于Bi，Sb抑制Al在晶界的偏聚，晶界区主要析出相为Mg₃Bi₂或Mg₃Sb₂，提高镁合金高温性能. 关键词： 电子理论 合金化 晶界偏聚 镁合组织与性能     

Y-Ba-Cu-O掺Ce体系的激光喇曼光谱

利用激光喇曼光谱分析了名义组分为(Y_1-xCe_x)Ba₂Cu₃O_7-δ(x=0,0.05,0.1,0.3,0.55,1.0)的系列样品的相组成,发现随着Ce的掺入,样品中除生成正交Y(123)相材料以外,还生成BaCeO₃和BaCuO₂等杂相。结果表明,Ce很可能根本没有替代Y生成Ce(123)相,而是和Ba生成了BaCeO₃杂质相 关键词：     

Gd3(Al,Ga)5O12:Ce闪烁晶体缺陷对其发光性能的影响

新型闪烁晶体Gd₃(Al,Ga)₅O₁₂:Ce(GAGG:Ce)在制备过程中易出现包裹体及反格位缺陷等问题,严重影响晶体的性能.为了抑制这些缺陷以得到大尺寸高质量的GAGG:Ce晶体,本文以Gd₃(Al,Ga)₅O₁₂为基质、Ce3+为掺杂离子,采用提拉法生长得到了GAGG:Ce晶体,并对不同晶体部位的物相结构、微区成分、透光性质、发光及时间性能进行了测试和对比分析.结果表明,GAGG:Ce晶体的透过谱中存在340和440 nm两处Ce³⁺特征吸收带,且位于550 nm处的直线透过率为82%.晶体尾部因杂相包裹体等宏观缺陷的影响,导致其透过率下降至70%左右.微区成分分析进一步表明GAGG:Ce晶体中存在三种类型的包裹体,分别为富Gd相、富Ce相及(Al,Ga)₂O₃相.GAGG:Ce晶体的X射线激发发射谱中在550 nm附近存在Ce³⁺宽发射带,且380 nm处还存在GdAl/Ga反格位缺陷引起的发射.晶体中存在的杂相包裹体及GdAl/Ga反格位缺陷等因素导致Ce³⁺在GAGG基质的发光强度下降12.5%;GdAl/Ga反格位离子与近邻Ce的隧穿效应使得GAGG:Ce晶体的衰减时间由117.7 ns延长至121.9 ns,且慢分量比例由16%增加至17.2%.     

ZnO-Bi2O3-Sb2O3-BaO系陶瓷的晶界相与抗退降性能

在通常的ＺｎＯ－Ｂｉ₂Ｏ₃－Ｓｂ₂Ｏ₃系电压敏陶瓷中，加入能构成压敏特性的钡添加剂，发现除已知的Ｂｉ₂Ｏ₃和Ｚｎ_2．３３Ｓｂ_０．６７Ｏ₄晶界相以外，还出现新的晶界相，分析表明是固溶有微量其它成分的偏锑酸钡（ＢａＳｂ₂Ｏ₆）晶相。同时还发现，ＢａＳｂ_{2关键词：}     

YAG：Ce发光材料合成的助熔剂研究

采用高温固相法合成YAG:Ce荧光粉时,传统的以硼酸为助熔剂的产物硬度很大,处理过程中容易破坏晶体形貌,影响发光性能.采用氟化物助熔剂(MgF₂、CaF₂、SrF₂、BaF₂、AlF₃)及它们与H₃BO₃混合助熔剂来制备YAG:Ce,研究了助熔剂种类及其浓度对制得的粉体发光性能的影响,比较了它们的晶体形貌与物相组成.结果表明,采用不同助熔剂合成的YAG:Ce的激发光谱及发射光谱基本相同,而BaF₂、AlF₃、SrF₂及它们与H₃BO₃的混合助熔剂系列,可在一定程度上降低产品硬度、提高产品发光亮度;其中H₃BO₃~SrF₂系列、H₃BO₃~BaF₂系列的晶化程度与粒度分布均有改善;H₃BO₃~BaF₂系列的物相组成比较纯,除Y₃Al₅O₁₂主相外基本无杂相.     

Mg-Sn-Si系合金的热力学基础及合金相演变过程分析

研究了Mg-Sn-Si系合金的热力学基础及合金相的演变过程. 结果表明: 对于Mg-Sn-Si系合金, 合金相的比热容随着温度增加而增加, 在低温下变化迅速, 而在高温下变化平缓, 其热膨胀系数在低温范围内随温度升高呈指数形式增加, 而在高温范围内呈线性增大. 在Mg₂ (Si_x, Sn_1-x)、Mg₂ (Sn_x, Si_1-x)相结构中, Sn(Si)原子的取代位置不固定, 可以是面心, 也可以是顶点. 常规凝固过程中, 由于处于非平衡状态, x的取值范围有所波动, 对于Mg₂ (Si_x, Sn_1-x)和Mg₂ (Sn_x, Si_1-x) 两种结构, x的取值范围在0.25或0.75附近. Mg₂ (Si, Sn)的生成温度较高, 可从液相中直接析出, 也可由Mg₂Si转化而来, 而Mg₂ (Sn, Si)的生成温度较低, 只能从基体中析出, 随着Sn含量的增加, 开始析出Mg₂ (Sn, Si)相的温度升高.     

SmCo5矫顽力与相变研究

用正电子湮没技术、1000kV超高压电子显微镜结合磁测量研究了SmCo₅永磁合金在回火中相析出和矫顽力机制。得出:从SmCo₅析出的Sm₂Co₁₇相本身不是反磁化形核中心,析出的Sm₂Co₁₇相中存在的某些多缺陷区域可以具有很低的磁各向异性,从而成为反磁化形核中心,使内禀矫顽力下降。实验中发现:SmCo₅从25℃到900℃回火,750℃出现最大磁不可逆损失。各种近邻Sm³⁺分布的中心Sm³⁺的磁各向异性随温度变化,越接近Sm₂Co₁₇结构,Sm³⁺为负磁各向异性的可能性越大。 关键词：     

Al-Ti-V-M四元系合金TiAl3-VAl3-MAl3(M=Ni,Fe)赝三元系相图的室温截面

本文用X射线衍射法测定了Al-Ti-V-M四元系合金TiAl₃-VAl₃-MAI₃(M=Ni,Fe)两个赝三元系相图的室温截面。(1)TiAl₃-VAl₃NiAl₃赝三元系相图室温截面由一个单相点ε(NiAl₃)、一个单相区δ(TiAl₃和VAl₃形成的连续固溶体)和一个两相区δ+s所组成。(2)TiAl关键词：     

在氧-水蒸气存在下单相Sr2(Gd,Ce)2Cu2RuO10的合成及其电学性质

传统固相反应所合成的锶系钌铜氧化物，通常总伴有少量铁磁性SrRuO₃杂相.采 用氧(或空 气)_水蒸气混合气氛下的新型固相反应，既能成功合成锶系钌铜氧化物的前驱物纯相Sr₂G dRuO₆(211相), 也能进一步在相对低的温度下成功合成锶系钌铜氧1222纯相化 合物RuSr₂(Gd,Ce)₂Cu₂O₁₀ (Ru_1222）， 使其中SrRuO _{关键词： 水蒸气参与的新型固相反应 2}(Gd')" href="#">RuSr₂(Gd 2Cu_{2< /sub>O10纯相')" href="#">Ce)2Cu2< /sub>O10纯相 3杂相')" href="#">SrRuO3杂相 电学性质}     

熔体快淬Pr(Fe1-xCox)2合金的结构和磁性

通过熔体快淬方法获得Pr(Fe_1-xCo_x)₂合金条带,经过X射线衍射、差示扫描量热计和磁性测量对其结构、磁性和热稳定性进行了研究.发现当Co的含量x大于0.2时才可能获得Pr(Fe,Co)₂立方Laves相化合物.对Pr(Fe_0.6Co_0.4)₂合金,在快淬速度为30m/s时,条带由Pr₂(Fe,Co)₁₇,Pr(Fe,Co)₂和富稀土相组成;在速度为40m/s时,获得了几乎单相的Pr(Fe_0.6Co_0.4)₂化合物,其居里温度为305℃;在速度为45m/s时,除了Pr(Fe_0.6Co_0.4)₂化合物外,还存在少量的非晶相.Pr(Fe_0.6Co_0.4)₂化合物在770℃以上发生分解.用40m/s快淬纳米晶粉胶粘磁体有大的磁致伸缩系数（λ_∥-λ_⊥=140×10^-6)和高的硬磁性能（_iH_c=398kA/m). 关键词：     

Theoretical studies of Ir5Th and Ir5Ce nanoscale precipitates in Ir

Experimentally, it is known that very small amounts of thorium and/or cerium added to iridium metal form a precipitate, Ir₅Th/Ir₅Ce, which improves the high-temperature mechanical properties of the resulting alloys. We demonstrate that there are low-energy configurations for nanoscale precipitates of these phases in Ir, and that these coherent arrangements may assist in producing improved mechanical properties. One precipitate/matrix orientation gives a particularly low interfacial energy, and a low lattice misfit. Nanolayer precipitates with this orientation are found to be likely to form with little driving force to coarsen. The predicted morphology of the precipitates and their orientation with the matrix phase provide a potential experiment that could be used to test these predictions.     

Ce(Ⅳ)和Ce(Ⅲ)化合物系列的X射线光电子能谱研究

用XPS研究了标称四价铈盐系列:硫酸铈铵、硫酸铈、二苯基羟乙酸铈、碘酸铈、过氧化铈、二氧化铈以及三价铈盐系列:草酸亚铈、硫酸亚铈、二苯基羟乙酸亚铈、碘酸亚铈和氯化亚铈.结果表明,上述标称四价铈盐都属于混合价化合物,其Ce3d电子能谱呈现Ce⁴⁺和Ce³⁺的二组谱线结构的混合.在真空中加热后CeO₂的Ols电子能谱有两个氧峰,这说明 Ce(4f⁰)O(2p^π)←→Ce(4f¹)O(2p^n-1) 类型价态波动的可能性较大.三价铈盐的3d谱线的低结合能端约3.5—4eV处则存在摔落伴峰.     

Spray-pyrolysis deposition of CeO2 thin films using citric or tartaric complexes as starting materials

Thin films of CeO₂ were deposited by spray-pyrolysis on β-quartz or optical grade silica glass substrates heated at 350–500 °C. Ethylene glycol solutions of Ce(NO₃)₃ and cerium citrates or tartrates (prepared using Ce(NO₃)₃ or CeCl₃ as cerium sources) were used as starting materials. Crystalline films may be obtained “in situ”. Post deposition annealing at 800 °C leads to bigger crystallites and cell constant closer to that of a reference material. The influence of the deposition temperature and the nature of the cerium compounds on the crystal structure and morphology of the films were studied.     

稀土元素Ce热引入Si单晶中及Ce在Si中的扩散系数

利用真空淀积和真空热处理(1050℃,20h)向Si单晶中引入了稀土元素Ce,热处理过程中Ce首先与Si形成合金,然后向Si中扩散,于是在Si中形成Ce的扩散层。用二次离子质谱(SIMS)技术测定了Ce的纵向相对浓度分布,并据此分析了Ce在Si中的扩散系数。并在77—450K范围内测量了扩散层的平均电导率。 关键词：     

Luminescence properties of CaS:Ce, Sm nanophosphors

CaS:Ce, Sm nanophosphors were synthesized via solid state diffusion method. X-Ray diffraction confirmed the cubic crystalline phase of CaS:Ce, Sm nanoparticles. The particle size calculated using Debye-Scherrer formula was found to be 52 nm. The morphological investigations of the nanoparticles were made using TEM and found to have nearly spherical morphology with diameter 45-50 nm, which is in close agreement with the XRD result. The PL emission characteristics of CaS:Ce, Sm as a function of cerium and samarium concentrations have been studied and CaS:Ce_0.6Sm_0.4 system has maximum emission intensity, hence it was opted for further studies. The CaS:Ce_0.6Sm_0.4 system showed independent emission of Sm and Ce when excited at 330 and 450 nm, respectively. To study the energy transfer between cerium and samarium, the CaS:Ce_0.6Sm_0.4 was excited at wavelengths other than the excitation wavelengths of Ce (450 nm) and Sm (330 nm). The existence of Ce emission (at an excitation of 390 nm) even in the absence of Ce excitation band and Sm emission at an excitation of 405 nm, which is the excitation band of Ce, indicates the energy transfer at these two wavelengths. Thermoluminescence characteristics of ⁶⁰Co irradiated CaS:Ce_0.6Sm_0.4 have been investigated for different doses of 0.14-125 Gy. All the glow curves show a single peak at 475 K. With increasing dose, the intensity of this peak increases and a shoulder is formed on the lower temperature side at 415 K at 21 Gy of exposure. CaS:Ce_0.6Sm_0.4 shows almost linear dose dependence up to 125 Gy.     

X-ray excited luminescence of Ce:Li2CaSiO4, Ce:CaBPO5 and Ce:LiCaPO4

Three materials Ce:Li₂CaSiO₄, Ce:CaBPO₅ and Ce:LiCaPO₄ were synthesized as polycrystalline samples for scintillation application in neutron detection. Ce³⁺ optical spectroscopy was investigated. Then, under X-rays excitation, Ce:Li₂CaSiO₄ and Ce:LiCaPO₄ present light yields about 7800 ph/MeV and 5900 ph/MeV, respectively. A self trapped exciton loss mechanism has been evidenced and competes with the cerium emission.     

Effect of Si addition on the valence state of Ce in CePd3

It is observed that Si can be added to CePd₃, which has the AuCu₃ type cubic structure, to form alloys of the type CePd₃Si_x where 0 ≤ x ≤ 0.3. Addition of Si preserves the structure but results in an expansion of the cell volume. The expansion is much larger in CePd₃ than in LaPd₃ for the same silicon concentration. In CePd₃, cerium is in a mixed-valent state and its susceptibility tends to a temperature independent value at low temperature. However, as Si is added to CePd₃, the susceptibility progressively increases and shows a Curie-Weiss behavior with effective moment close to that of Ce³⁺ ions. Thus from lattice parameters and susceptibility measurements, it is inferred that Si addition causes a change in the valence of Ce in CePd₃ from mixed valent to nearly trivalent.     

Valence instability of Ce and La impurities in YNi2

Measurements of resistivity and lattice constants are reported for the Y_0.98RE_0.02Ni₂ series of alloys. Both the Ce and the La alloys show strong anomalies in volume and resistivity increment, especially at low temperatures. This is the first indication for a valence instability on an impurity of La.     

Ultrasonic-assisted synthesis of Ce doped cubic–hexagonal ZnTiO3 with highly efficient sonocatalytic activity

Ce doped ZnTiO₃ as a novel catalyst with highly efficient and stable sonocatalytic activity was synthesized via an ultrasound-assisted sol–gel method using non-ionic surfactant Pluronic F127 as structure directing agent. Synthesized samples were characterized by using various techniques, such as XRD, TEM, SEM, EDX, ​XRF, BET, DRS, and PL, and their sonocatalytic activity studied toward degradation of p-Nitrophenol as a model organic compound. The synthesized mesoporous Ce/ZnTiO₃ had mixed cubic–hexagonal phase with large surface area (118.2 m² g^–1) and narrow pore size distribution (4.9 nm). The effects of cerium concentration, calcination temperature, and calcination time on the structure and the sonocatalytic activity of Ce/ZnTiO₃ were studied in detail. XRD results were suggested that the relation between the phase structure and the catalytic activity is considerable. Significant decrease in band-gap and PL intensity was observed with increasing the cerium concentration in the ZnTiO₃. It became clear that the Ce/ZnTiO₃ (0.81 mol%) shows high sonocatalytic activity compared with pure ZnTiO₃ and other Ce/ZnTiO₃ samples as well as commercial TiO₂-P25. The possible mechanism for the enhanced sonocatalytic activity of Ce/ZnTiO₃ was discussed in details. The electrical energy consumption was also considered during sonocatalytic experiments.     

Superconducting transition temperature,its pressure dependence and structural transformation in (La,Ce)Ru2 alloys

The superconducting transition temperature and its dependence on hydrostatic pressure to 22 kbar have been determined for a series of (La, Ce)Ru₂ alloys. The variations of these quantities with composition are found to be generally related; however, specific irregularities in the curve of dT_c/dp versus composition are not reflected in the smooth variation of the transition temperature T_c. Some features of dT_c/dp may be correlated with the occurrence of a cubic-tetragonal transformation at low temperatures.