Compression and shear on lead in a rotational diamond anvil cell

By application of large plastic shear on a lead sample in a rotational diamond anvil cell, we studied the pressure self-multiplication and the stress deviation phenomena, along with the consequential effects on a phase transformation of lead. It is indicated that pressure can be promoted by the gradual addition of shear. The stress deviation in the sample along different Chi angles is minimal and within the systematic error range. It is thus specified that a quasi-hydrostatic condition is generated in the sample chamber. Moreover surprisingly, under such shear-controlled pressure elevation, the lead fcc-to-hcp phase transformation pressure is found to initiate and complete, respectively, at 12.8 and 18.5?GPa, which is identical to those observed in hydrostatic compressions. The phenomena of the so-launched quasi-hydrostatic pressure, the self-multiplication, along with the consequential effects on the phase transformation properties by shear at pressures are expected to lead to further understanding of materials as well as to potential new technologies at extremes.     

Prediction of a superhard material of ReN4 with a high shear modulus

Using first-principles calculations, this paper systematically investigates the structural, elastic, and electronic properties of ReN 4 . The calculated positive eigenvalues of the elastic constant matrix show that the orthorhombic P bca structure of ReN 4 is elastically stable. The calculated band structure indicates that ReN 4 is metallic. Compared with the synthesized superhard material WB 4 , it finds that ReN 4 exhibits larger bulk and shear moduli as well as a smaller Poisson’s ratio. In addition, the elastic constant c 44 of ReN 4 is larger than all the known 5d transition metal nitrides and borides. This combination of properties makes it an ideal candidate for a superhard material.     

Spin-glass-like behavior of uncompensated surface spins in NiO nanoparticulated powder

Nickel oxide nanoparticles successfully synthesized by a polymer precursor method are studied in this work. The analysis of X-ray powder diffraction data provides a mean crystallite size of 22±2 nm which is in a good agreement with the mean size estimated from transmission electron microscopy images. Whereas the magnetization (M) vs. magnetic field (H) curve obtained at 5 K is consistent with a ferromagnetic component which coexists with an antiferromagnetic component, the presence of two peaks in the zero-field-cooled trace suggests the occurrence of two blocking process. The broad maximum at high temperature was associated with the thermal relaxation of uncompensated spins at the particle core and the low temperature peak was assigned to the freeze of surface spins clusters. Static and dynamic magnetic results suggest that the correlations of surface spins clusters show a spin-glass-like behavior below T_g=7.3±0.1 K with critical exponents zν=9.7±0.5 and β=0.7±0.1, which are consistent with typical values reported for spin-glass systems.     

Magnetic behavior and physicochemical properties of Ni and NiO nano-particles

A series of nano-crystalline Ni/NiO particles was synthesized by a combustion route depending upon the glycine-nitrate process. The as prepared samples were characterized by X-ray diffraction (XRD), scanning electron micrograph (SEM), transmission electron micrograph (TEM), nitrogen adsorption isothems at 77 K and vibrating sample magnetometer (VSM) techniques.The XRD results revealed that the Ni powder crystallizes was formed with the cubic phase when the molar ratio of glycine to nitrate is 1.5. Above or below that molar ratio, NiO phase coexists as an impurity along with the Ni phase. The SEM and TEM measurements of the as synthesized powders showed that the particles are irregular in shapes and have porous morphology. Increasing the ratio between glycine and Ni-nitrate resulted in slightly agglomeration and grain growth of nano-particles with subsequent decrease in the value of surface area depending upon high combustion heat. The magnetization value of Ni measured at room temperature is very close to the value observed for commercial Ni powder.     

Exchange bias and training effect in Ni/Ag-doped NiO bilayers

A series of polycrystalline Ag-doped Ni_1−xAg_xO/Ni bilayers with x up to 0.2 were prepared by magnetron sputtering. X-ray diffraction, atomic force microscopy and transmission electron microscopy analyses reveal that Ag doping significantly reduces the mean NiO grain size and leads to the appearance of Ag nanoparticles on the surface of the Ag-doped NiO films. As x increases, the exchange bias field and coercivity at room temperature decrease as a consequence of the reduced thermal stability of smaller NiO grains and the screening effect resulting from the interfacial Ag nanoparticles. At lower temperatures, a slight enhancement of the exchange bias field is observed in the Ag-doped sample, indicating that the Ag doping increases the uncompensated NiO spin density. In addition, our studies find that the training effect of the Ag-doped sample can be well described by a spin configurational relaxation model, regardless of the presence of Ag nanopartiles at the interface.     

Elastic moduli of hard c‐Zr3N4 from laser ultrasonic measurements

The bulk and shear moduli of dense polycrystalline oxygen‐bearing c‐Zr₃N₄ were determined to be B₀ = 217(20) GPa and G₀ = 163(9) GPa, respectively, using laser ultrasonic technique combined with a numerical analysis of the sample porosity. While the obtained B₀ is in excellent agreement with the earlier high‐pressure compression measurements, the G₀ value is 70% higher than the previous estimate. Since both G₀ and hardness of the dense c‐Zr₃N₄ exceed those of γ‐Si₃N₄, c‐Zr₃N₄ vies for the rank of the third hardest material after diamond and cubic BN. Our results also support the suggestion that shear modulus is a robust predictor of hardness. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Al、Cu、Ta高压熔化曲线的理论计算

由位错熔化理论和不同的静高压实验数据优化的体模量(B0)、剪切模量(G0)及它们对压力的一阶偏导数(B′0、G′0)值计算了Al、Cu、Ta的高压熔化曲线.理论计算的Al、Cu高压熔化曲线与静、动高压实验值较为吻合,Ta的理论高压熔化曲线与动高压实验结果一致,但与静高压实验结果相差较大.     

Nanoscale resistive random access memory consisting of a NiO nanodot and Au nanowires formed by dip-pen nanolithography

We demonstrate the nanoscale resistive random access memory (RRAM) element consisting of an approximately 30 nm diameter NiO nanodot and two bridging Au nanowires, formed by a dip-pen nanolithography technique using nickel carbonate (Ni₂(CO₃)(OH)₂) and [AuCl₄]⁻ complex solutions, respectively. The Au/NiO/Au nanowire resistive switch exhibits typical unipolar switching characteristics with high performance at low Set and Reset voltages.     

Temperature and set field dependence of exchange bias training effects in Co/NiO/[Co/Pt] heterostructures with orthogonal easy axes

Training effects in a new class of exchange biased ferromagnet/antiferromagnet/ferromagnet trilayers (Co/NiO/[Co/Pt]₃) with mutually orthogonal easy axes have been measured and successfully modeled. Previous experiments have demonstrated an enhanced blocking temperature as well as the ability to isothermally field tune the magnitude of the room temperature in-plane exchange bias. These effects have been attributed to the presence of the [Co/Pt] multilayer with perpendicular magnetic anisotropy, which variably pins the backside NiO domains. Here we show that the tuning of the exchange bias and the blocking temperature enhancement are highly dependent on both the temperature and the in-plane remanence of the normally out-of-plane [Co/Pt] multilayer, achieved using modest in-plane set fields. Training effects and their dependence on temperature and in-plane remanence are modeled using a thermodynamic approach. The in-plane remanence of the [Co/Pt] acts only to set the equilibrium exchange bias value and sets the scale for the blocking temperature; it has no effect on the training. We conclude that training effects occur only at the Co/NiO interface and that the relaxation towards equilibrium is confined to this interface. The field enhanced blocking temperature and isothermal tuning of exchange bias in these magnetic heterostructures with mutually orthogonal easy axes could play a role in the enhancement of exchange bias effects in future spin-valve devices. A thorough knowledge of the training effects is essential to account for the fundamental relaxation mechanisms that occur with repeated field cycling.     

冲击加载下Zr51Ti5Ni10Cu25Al9金属玻璃的塑性行为

进行了10—27 GPa应力范围内Zr₅₁Ti₅Ni₁₀Cu₂₅Al₉金属玻璃的平面冲击实验以研究其高压-高应变率加载下的塑性行为.由样品自由面粒子速度剖面的分析获得了冲击加载过程的轴向应力,并通过轴向应力与静水压线的比较获得剪应力.实验结果表明,尽管存在明显的松弛效应,但Zr基金属玻璃的Hugoniot弹性极限随着冲击应力的增加而增加.然而,塑性波阵面上的剪应力则显示先硬化而后软化现象,而且软化的幅度随冲击应力的增加而增加.冲击加载下Zr基金属玻璃的上述剪应力变化特征与分子动力学模拟结果比较一致,但与压剪实验结果和一维应力冲击实验结果明显不同.     

第2届全国大学生物理实验竞赛试题的解答与考试评析(续)

<正>3综合性、研究性试题的解答与评析第二届全国大学生物理实验竞赛的综合性、研究性试题为"磁光效应的研究"和"磁流体性质的研究"两题.目的是综合考察考生对不同物理实验手段的理解、掌握水平和综合分析应用能力.各代表队由2人合作完成,时限8h.3.1试题1磁光效应的研究(时限4h)3.1.1引言磁流体是指磁性纳米颗粒在表面活性剂进行包覆或改性后,均匀分散到载液中,形成稳定的胶体溶液.外加磁场时,磁流体中的磁性微粒会顺     

纳米Ni在77 K温度下压缩行为的研究

利用低温力学测试系统研究了电化学沉积纳米Ni在77 K温度下的压缩行为. 室温下纳米Ni 的屈服强度为 2.0 GPa, 77 K温度下的屈服强度为3.0 GPa, 压缩变形量则由室温的10%左右下降到5%. 借助应变速率敏感指数、激活体积、扫描电子显微和高分辨透射电子显微分析, 对纳米Ni的塑性变形机制进行了表征. 研究表明, 在77 K温度下的塑性变形主要是由晶界-位错协调变形主导, 晶界本征位错弓出后无阻碍地在晶粒内无位错区运动, 直至在相对晶界发生类似切割林位错行为. 同时分析了弓出位错的残留位错部分在协调塑性变形时起到的增加应变相容性和减小应力集中的作用. 利用晶界-位错协调机制和残留位错运动与温度及缺陷的相关性揭示了纳米Ni室温和77 K温度压缩性能差异的内在原因. 关键词： 塑性变形 强度 位错     

Interactions of NiO particles with polycyclic aromatic hydrocarbons and acetylene generated from the pyrolysis of a model fuel

Experiments have been conducted to study the effects of NiO, a prevalent form of nickel in combustion-generated ash particles, on polycyclic aromatic hydrocarbons (PAH) and other hydrocarbons in a fuel product mixture. The fuel product mixture is generated from the gas-phase pyrolysis, in N₂, of the model fuel catechol in a quartz tube reactor at 1100 K and 5 s, a condition that ensures full conversion of the catechol and produces a mixture—of PAH, hydrocarbon gases, and oxygen-containing species—that is representative of the products of practical liquid and solid fuels in pyrolysis and fuel-rich combustion environments. Once formed, the product mixture is passed, at the same temperature, through a bed of ultrafine NiO particles held in place by quartz wool, in the contact zone of the reactor. The products exiting the reactor are quenched, collected, and analyzed by non-dispersive infrared analyzers, gas chromatography, and high-pressure liquid chromatography with diode-array ultraviolet–visible absorbance detection. The results from the experiments at 1100 K show that—compared to the case of no inorganics in the contact zone—when NiO is present: PAH yields are reduced 86% (from 10.8% to 1.48% fed carbon); all of the highly mutagenic 5- and 6-ring PAH are eliminated; and all of the acetylene, the highest-yield hydrocarbon product when NiO is absent, and other hydrocarbons with carbon–carbon triple bonds are eliminated from the gas phase. Most of the surface-bound carbon is released as CO. Similar experiments at 1275 K show that—except for the release of the surface-bound carbon as CO—the selective surface effects of NiO bring about similar results at higher temperature: 89% reduction in PAH yield, elimination of mutagenic 5- and 6-ring PAH, removal of acetylene and acetylenic species, as well as a decrease in the production of solid carbon (not formed at 1100 K).     

Study on new magnetization property and its micro‐mechanism that occurred in anti‐ferromagnetic NiO nanoflowers with nearly uniform size

Temperature‐dependent magnetization and magnon Raman spectra were measured for anti‐ferromagnetic NiO‐nanoflowers. The results show several new magnetic behaviors, including the appearance of a ferromagnetic phase, a reduced Néel temperature (T_N) and a reduced Curie temperature (T_C). The temperature dependencies of the double magnon (2M) Raman wavenumber and intensity are similar to those of magnetization. A magnetic granules model (MGM) consisted of a crystalline core enclosed by a shell is proposed. The model suggests that the large quantity of spins induced by specific surface effect in the shell plays a key role in nano‐magnetism. Based on the MGM, the micro‐mechanism of the observed new magnetic behavior is understood by the magnon Raman spectra. The MGM is based on the general features of magnetic nano‐particles, and thus it should be generally applicable to common magnetic nano‐particles. Copyright © 2014 John Wiley & Sons, Ltd.     

Elastic moduli of η‐Ta2N3, a tough self‐healing material,via laser ultrasonics

The elastic moduli of the dense polycrystalline oxygen‐bearing η‐Ta₂N₃, a novel hard and tough high‐pressure (HP) material, were measured using the laser ultrasonic technique. The bulk modulus was determined to be B₀ = 281(15) GPa which is only ～11% below that from HP compression measurements. Our value of the shear modulus G₀ = 123(2) GPa is below those ones predicted theoretically for model structures. The discrepancies in G₀ could be due to a substitution of an‐ ions and the formation of cation vacancies in η‐Ta₂N₃. Self‐healing behaviour of η‐Ta₂N₃ by mechanical polishing was observed and confirmed by two independent experimental methods. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Exploring the compression behavior of HP-BiNbO_4 under high pressure

In the present work, a third form, the so-called HP-BiNbO_4 synthesized at high pressure and high temperature is investigated with the in-situ angle-dispersive x-ray diffraction(ADXRD) measurements under high pressure. We explore the compression behavior and phase stability of HP-BiNbO_4. The structure of HP-BiNbO_4 is first determined. The x-ray diffraction data reveal that the structure HP-BiNbO_4 is stable under pressures up to 24.1 GPa. The ADXRD data yield a bulk modulus K_o = 185(7) GPa with a pressure derivative K_o'= 2.9(0.8). Furthermore, the data are compared with those of other ABO_4 compounds. The results show that the bulk modulus of HP-BiNbO_4(about 185 GPa) is slightly higher than that of tetragonal BiVO_4 and significantly greater than those of the tungstates and molybdates.     

冲击压缩下铝、铜、钨的剪切模量和屈服强度与压力和温度的相关性

对铝、铜和钨在冲击压缩状态下的剪切模量和屈服强度的实验数据进行了综合分析，并与St einberg-Cochran-Guinan(SCG)模型的计算结果进行了比较，结果表明，铝在50 GPa、铜在1 00 GPa、钨在200 GPa冲击压力以内，三种材料的剪切模量和屈服强度随温度和压力的变化 趋势基本相似，即SCG模型的假设Y′_pY₀=G′_pG ₀,Y′_TY₀=G′_TG₀对这三种材料在上述冲击压力范围内近似成立，利用该模型可以较好地描述材料在冲击压缩 下的本构行为. 关键词： 剪切模量 屈服强度 压力 温度     

Deformation behavior of Fe-based bulk metallic glass during nanoindentation

Fe-based bulk metallic glasses (BMGs) normally exhibit super high strength but significant brittleness at ambient temperature. Therefore, it is difficult to investigate the plastic deformation behavior and mechanism in these alloys through conventional tensile and compressive tests due to lack of distinct macroscopic plastic strain. In this work, the deformation behavior of Fe₅₂Cr₁₅Mo₉Er₃C₁₅B₆ BMG was investigated through instrumented nanoindentation and uniaxial compressive tests. The results show that serrated flow, the typical plastic deformation feature of BMGs, could not be found in as-cast and partially crystallized samples during nanoindentation. In addition, the deformation behavior and mechanical properties of the alloy are insensitive to the applied loading rate. The mechanism for the appearance of the peculiar deformation behavior in the Fe-based BMG is discussed in terms of the temporal and spatial characteristics of shear banding during nanoindentation. Supported by the National Natural Science Foundation of China (Grant Nos 50571109, 10572142 and 56771102) and the National Basic Research Program of China (973 Program)(Grant No 2007CB613900)     

The critical behavior of shear modulus in solid-liquid mixing phase

The behavior of shear modulus in solid-liquid mixing phase has been discussed and analyzed. The result was concluded that shear modulus went to zero as the melting mass ratio attained a critical value. The percolation theory model we proposed showed that this value was about 0.68742. The melting-induced destabilizing factor of material proposed by us can represent phenomenologically the change of shear modulus in melting process.     

NiO透明导电薄膜的制备及在聚合物太阳能电池中的应用

采用磁控溅射法制备出透明导电氧化物NiO薄膜.椭偏(SE)测试表明NiO薄膜在可见光区域透光性良好,通过调节生长、退火温度可调控NiO的折射率.采用X射线衍射(XRD)、扫描电子显微镜(SEM)手段研究表明,通过退火、改变衬底温度等,可有效改变NiO薄膜的晶体结构以及表面形貌,实现对NiO导电性的调控. 采用优化后的NiO材料为阳极阻挡层制备出的聚合物太阳能电池器件的效率为2.26%,是同等条件下采用 PEDOT:PSS阻挡层的电池器件的3倍以上.