非晶材料的热膨胀系数和声子谱测量与纳米晶成形机制的关联

用熔体快淬法制备的非晶态合金经退火处理可形成纳米晶合金,其形成机制至今仍是研究的热点。国外纳米晶成形机制研究主要集中在添加元素在晶核的形成和长大过程中的作用等方面。本工作认为纳米晶的形成有着更深层的原因,结合长期以来关于因瓦合金的热膨胀系数和声子谱测量,以及最近纳米软磁材料的声子谱研究,指出非晶态合金中的声子软化现象反映出原子间的相互作用力减弱,非晶合金体系处于结构松散状态,非晶合金的这种结构不稳定性才是造成其在晶化初期易于爆发式大量形核,并进一步形成均匀分布的纳米晶的主要原因。     

高温原位XAFS研究NiB纳米非晶态合金催化剂的结构

原位XAFS方法研究NiB纳米非晶态合金在78K至573K温度范围的结构特点。结果表明：在78K时,NiB样品的第一配位峰的位置和强度分别为2．06A、396.4,其强度只有Ni箔第一配位峰强度的25％左右;300K时,第一配位峰的位置和强度分别2．08A、255．9;573K时,第一配位峰的位置和强度分别为1．87A、155．4。温度从78K升至300K,第一配位峰的位置变化不大,但峰强度降低35％左右;温度继续升至573K时,冷的位置较78K的向小的方向移动0．20A,并且强度降低了60％。这表明随着测量温度的升高,NiB纳米非晶态合金中Ni原子周围的热无序度显增加。     

高温原位XAFS研究NiB纳米非晶态合金催化剂的结构

原位XAFS方法研究NiB纳米非晶态合金在78K至573K温度范围的结构特点。结果表明：在78K时，NiB样品的第一配位峰的位置和强度分别为2．06A、396．4，其强度只有Ni箔第一配位峰强度的25％左右；300K时，第一配位峰的位置和强度分别2．08A、255．9；573K时，第一配位峰的位置和强度分别为1．87A、155．4。温度从78K升至300K，第一配位峰的位置变化不大，但峰强度降低35％左右：温度继续升至573K时，峰的位置较78K的向小的方向移动0．20A，并且强度降低了60％。这表明随着测量温度的升高，NiB纳米非晶态合金中Ni原子周围的热无序度显增加。     

一种Zr基核材料的制备工艺、结构及力学性能研究

采用直流磁控溅射法在纯Zr基片上制备ZrCu非晶合金膜形成复合材料,可望作为潜在的核材料。运用扫描电镜、能谱仪、X射线衍射仪、高分辨透射电子显微镜对其结构表征,最终选用非晶成分Zr65Cu35。对以Zr65Cu35成分合金靶制备的非晶膜及其镀覆在Zr基片上形成的复合材料分别进行力学性能测试。结果表明,ZrCu成分在Zr40Cu60-Zr80Cu20之间均为非晶基体,略含有少量的纳米晶颗粒,纳米晶颗粒尺寸在10 nm以下。且当Zr含量增加时,非晶馒头峰的中心位置由45不断左移,直到~31。另外,Zr65Cu35合金靶溅射时间为30 min的薄膜硬度最大,稳定时为7.7 GPa,其杨氏模量均稳定在~110 GPa,镀膜复合材料与相同尺寸的纯Zr基片相比,其抗弯强度、抗拉强度及塑性形变均有提高。     

块体非晶合金Zr55Cu30Al10Ni5玻璃转变温度附近晶化的同步辐射X光小角散射研究

应用同步辐射X光小角散射法对块体非晶合金Zr55Cu30Al10Ni5在玻璃转变温度附近的晶化进行研究。实验表明：在400—442℃的退火温度范围内,样品中已有结晶颗粒析出,析出颗粒的大小差别不明显,但析出颗粒的数量与退火温度及退火时间有关。退火时间一定时,析出的颗粒数量随退火温度的升高而增多：退火温度一定时,析出的颗粒数量随退火时间的增加而增多。     

用离子束技术研究稀磁半导体和纳米磁性材料

综述用离子束技术研究稀磁半导体和纳米磁性材料的构建、调控和改性的进展和现状。离子束注入是优选的构建和调控方法,测试结果表明在GaN和ZnO等新半导体光电材料中注入Mn、Ni和Co等过渡金属离子可得到低温和室温下的铁磁性。离子束分析技术给出这些新材料薄膜的微结构信息,透射电镜下观察到过饱和剂量Mn+注入GaN形成的纳米磁性颗粒。     

钍基熔盐堆238群中子-48群光子耦合库的研制

为满足新一代核能系统钍基熔盐堆核设计用AMPX格式多群中子-光子耦合常数库的需求,基于为钍基熔盐堆推荐的微观评价核数据库CENDL-TMSR和ENDF/B-Ⅶ.1热散射数据子库及光子-原子相互作用数据子库,采用中子-光子耦合群常数制作系统NPLC-2研制了一套AMPX格式的238群中子-48群光子耦合多群常数库。该库包含400个核素、12种热散射材料,温度从300~2 500K共5个温度点。该库采用窄共振近似进行共振自屏处理,重点锕系核素支持Nordheim方法处理共振自屏。经初步的临界基准验证和屏蔽基准验证,证明了该库的可靠性。     

低温环境下霍尔探头标定

利用高精度低温霍尔探头可以测量永磁体在低温环境下的磁性能,如何对高精度霍尔探头在低温环境下进行精确标定对于永磁体低温磁性能研究有着重要意义。上海光源磁测实验室在霍尔探头常温标定的基础上,利用小型制冷机把霍尔探头置于液氮温区,通过在制冷机冷头上安装精确控制的电加热器可调节测试温度(6.5-300 K),并实现恒温。初步标定实验结果表明,低温霍尔探头灵敏度随着温度的下降逐渐上升,在50 K以下趋于平缓,相比常温灵敏度增大约4%。标定后的该探头可以测量低温环境下永磁体的磁性能,并可满足永磁体在低温环境下的性能研究需求。     

CdMnS的制备及其铁电铁磁性研究

用共蒸发的方法制备了六角多晶结构的CdMnS薄膜,研究了薄膜的铁电性和铁磁性.2%Mn浓度的样品的剩余极化强度Pr为1.72μC/cm2,矫顽场强Ec为14.3kV/cm.Au掺杂的CdMnS样品的居里点超过了300K.在10K低温磁滞回线中,得到的剩余磁化强度和磁矫顽力分别为1.39×10-6emu和75.4 G;用磁力显微镜清楚地观察到从几个纳米到一百纳米大小不等的磁性团簇,还发现掺杂元素的浓度对其磁性具有明显影响.     

欧姆加热蒸镀Y-Ba-Cu-O薄膜的超导电性及其各向异性

我们利用欧姆加热共蒸发的方式,首次制备出了液氮温度以上的YBa_2CuO_(7-δ)超导薄膜。目前得到的结果是:起始超导转变温度95K;零电阻温度78.6K;转变宽度ΔT_c=12K。不同参量的测量结果表明,样品具有明显的各向异性。电阻测量表明,在超导转变前,电阻有一 谷值,我们认为这与电子局域化和氧原子的迁移有关。     

Effect of γ-irradiation on the temperature coefficient of surface resistivity of two-dimensional island platinum films

Three sets (A, B and C) of two-dimensional island platinum films (2D-I(Pt)Fs) were prepared via the thermal evaporation technique, where the substrates are corning 7059 glass slides. The mass thickness (d_m) of the films of different sets is 5, 10 and 20 Å, respectively. The Pt films were exposed to γ-rays from ¹³⁷Cs (0.662 MeV) radiation source of dose rate 0.5 Gy/min. and the different doses are 100, 200, 300, 500 and 700 Gy. The dependence of the surface resistivity (ρ) on temperature over the range of 100-300 K was undertaken at different d_m and doses then the temperature coefficient of surface resistivity (α) was deduced. It was found that; (i) for particular d_m and T, the absolute value of α decreases as the dose increases (ii) for particular dose and T, the absolute value of α decreases as d_m increases (iii) for particular dose and d_m, the absolute value of α decreases as T increases. Qualitative interpretation for the results was offered on the ground that the electrons transfer among islands takes place by the activated tunneling mechanism and the γ-irradiation has changed the shape of islands from spherical to prolate spheroid.     

U—10Zr合金的电阻率,热导率和相变

用四端引线法测量了Ｕ－１０Ｚｒ（即Ｕ０．７７Ｚｒ０．２３）合金在３００－１３０Ｋ温度范围的电阻，计算出了此温度范围的电阻率。由电阻率－温度由线得到４个相变温度，分别为８８１、９３７、９７１和９９０Ｋ。根据Ｗｉｅｄｅｍａｎｎ－Ｆｒａｎｚ定律计算了各温度的热导率值，它在８８０Ｋ以下的激光脉冲法得到的热导率值符合得很好。在８８０Ｋ以上的值和Ｌｅｉｂｏｗｉｔｚ等得到的Ｕ０．７５Ｚｒ０．２５的热导率值相一致     

MD simulation of atomic displacements in pure metals and metallic bilayers during low energy ion bombardment at 0 K

Molecular Dynamics (MD) simulations of 100 eV Ar ion bombardment of (1 0 0) Ni and Al crystals, of bilayer crystals consisting of an Al (or Ni) layer on a (1 0 0) Ni (or Al) substrate, as well as pseudo-isotope bilayer crystals have been performed at 0 K using tight-binding potentials. For these systems sputtering yields, energy deposition with depth, atomic relocations, production of ad-atoms, depth distributions of vacancies and interstitials per ion impact were studied for times up to 7 ps. We observed that both the mean square displacement of atoms and defect production (vacancies, interstitials and ad-atoms) are larger in pure Al than in pure Ni. In addition, we observed for the bilayer systems Al/Ni and Ni/Al a high number of the near surface atomic relocations; especially ion bombardment induced exchange processes between atoms of the 1st (Al or Ni) and of the 2nd (substrate) layer. Potential energy calculations indicate that such relocations between the 1st and the 2nd layer are in both bilayer crystals energetically favourable. Both Al/Ni and Ni/Al bilayers show considerable higher production of ad-atoms as the pure Al and Ni targets. Typically ad-atoms are from the first layer, but in the Ni/Al bilayer system we found a substantial amount of Al ad-atoms from the 2nd layer (first Al layer). They contribute more to the ad-atom number than 1st layer Ni atoms. The mean square displacement of atoms in Al/Ni and Ni/Al crystals increases considerably during the thermal stages of the cascade evolution while it is almost constant in the case of the pure Al and Ni. Finally we observed that the maximum kinetic energies of atoms in the cascade volume after 4 ps are lower in the Ni and Al/Ni crystals than in Al and Ni/Al crystals, reflecting the lower cohesive energy of Al as compared to Ni. Calculations with pseudo-isotope bilayer crystals were performed to elucidate the influence of mass or potential on the observed effects.     

Isochronal recovery of fast neutron irradiated metals

The isochronal recovery of Al, Ni, Cu, Ag. Au, Pt, Fe, Mo and Co, irradiated at 4.5K with fast neutrons has been studied resistometrically. For the face-centered cubic elements, Al, Ni, Cu, Ag, and Au, the magnitude of stage I recovery is inversely proportional to the atomic mass of these elements, which is in excellent agreement with recent calculations on the spatial distribution of lattice defects in fast neutron irradiated metals. The total irradiation-induced resistivity and hardness of neutron spectra have more of an influence on the details of the recovery stages than does the initial residual resistivity and the initial resistivity ratio. Stage II recovery, at least in Cu, can be explained best by the rearrangement and/or annihilation of defects that are released from the stress fields of the vacancy clusters that exist in fast neutron irradiated metals.     

Radiation-induced separation of solid solution in Fe-Ni invar

Radiation-induced solid solution separation (RISSS) in the Fe-34.7 at.% Ni invar alloy was investigated by residual resistivity and linear thermal expansion coefficient (TEC) measurements. The alloy was irradiated with 5 MeV electrons at 245-570 K and isochronous annealed. It was found that RISSS leads to an increase of 20% in the residual resistivity and an increase of 10⁻⁵ K⁻¹ in the TEC for an electron irradiation dose of 5 × 10¹⁸ cm⁻². The kinetics of RISSS are the same, but the irradiation efficiency coefficient increases approximately by a factor of 10 when the irradiation temperature rises in the range of 240-570 K. Vacancy clusters, which are formed under irradiation, retard the decomposition. It was shown that dissociation of the vacancy clusters at temperatures of 320-500 K was followed by the free migration of the formed vacancies, and leads to further RISSS.     

In-reactor stress relaxation of selected metals and alloys at low temperatures

Sttess relaxation of bent beam specimens under fast neutron irradiation at 340 and 570 K has been studied for a range of materials, as follows: several stainless steels, a maraged steel, AISI4140, Ni, Inconel X-750, Ti, Zircaloy-2, Zr-2.5% Nb and Zr₃ Al. All specimens were in the annealed or solution-treated condition. Where comparisons were possible, the creep coefficients derived from the stress relaxation tests were found to be consistent with other studies of irradiation-induced creep. The steels showed the lowest rates of stress relaxation; the largest rates were observed with Zr-Nb, Ti and Ni. For most materials, the creep coefficient at 340 K was equal to or greater than that at 570 K. Such weak temperature dependence is not easily reconciled with existing models of irradiation creep based on dislocation climb, such as SIPA or climb-induced glide. Rate theory calculations indicate that because the vacancy mobility becomes very low at the lower temperature, recombination should dominate point defect annealing, resulting in a very low creep rate compared to that at the higher temperature. It is shown that the weak temperature dependence observed experimentally cannot be accounted for by the inclusion of more mobile divacancies in the calculation.     

Influence of oxygen on the production and recovery of defects in low-temperature deformed zirconium

The production and elimination of defects in high-purity zirconium and in oxygen doped zirconium (750 and 1100 × 10⁻⁶ at.), deformed by torsion at 4.2 K, were investigated by using electrical resistivity measurements. In all types of samples, the resistivity produced by cold-work increases linearly with shear strain. The rate of increase in resistivity is more important in oxygen doped zirconium than in the pure metal (it is multiplied by a factor of about 2.5). This increase in resistivity increment was attributed to an effect of oxygen on the deformation mechanisms. An important fraction of the excess of resistivity produced by deformation in the Zr-O dilute alloys anneals at about 35 K. The amplitude of this recovery stage increases with oxygen content and might be due to the elimination of the supplementary defects induced by oxygen atoms. Several small recovery stages were observed up to room temperature in pure zirconium and the addition of oxygen appears to have little effect on them.     

Helium diffusion behavior and its retention in LaNiAl alloy from molecular dynamic simulations

Molecular dynamic method has been used to investigate the diffusion behavior of helium atom in the LaNiAl alloy system. The results have shown that diffusion coefficient of helium atom increases as the temperature increases from 300 to 1500 K, which indicates that helium atom gets more active via thermal desorption. The diffusion coefficient in LaNi₅ and LaNi₄Al are about 1.5 × 10⁻⁵ and 1.1 × 10⁻⁶ cm²/s at 1300 K, respectively, and the diffusion barrier of He are 1.45 and 0.52 eV, respectively. The helium diffusion is shown to be enhanced with temperature increasing. Compared with metallic La, Ni, Al and Pd, the simulation result implies that helium atom is more stable and difficult to diffuse in LaNi₅ and LaNi₄Al alloys, which are the most promising materials for helium retention in experiments. Our results indicate the correlation between diffusion behavior of helium atom and capacity of materials for helium retention. Therefore, it can be considered as a feasible method to evaluate the helium retention capacity of materials via determining the diffusion properties of interstitial helium atom.     

Minority Carrier Recombination in Neutron Irradiated Silicon

Measurements are reported which provide extensive data on the resistivity, temperature, and injection level dependences of the minority carrier lifetime in neutron irradiated p- and n-type silicon. The lifetime damage constants are observed to be quite dependent on the injected minority carrier density, in both conductivity types, over the temperature range from 76°K to 300°K. The low injection level damage constants have been measured and found to be dependent on material resistivity in p-type silicon, but only slightly dependent on resistivity in n-type silicon. The results of the experimental studies are compared to the predictions of two alternate models for recombination at defect clusters. For defect clusters of approximately 250 A radius, as expected from range calculations, these comparisons indicate that each contains a relatively small number of deep defects (30 - 40). The defects are individually characterized by a deep donor level near Ev + 0.35 eV and a deep acceptor level near Ec - 0.50 eV. Since these levels correspond approximately to the known energy levels of the silicon divacancy, it is suggested that the divacancy may be the active recombination center within the defect clusters.