非晶态Mg70Zn30合金结构因子的预峰

利用X射线衍射仪对非晶态Mg₇₀Zn₃₀合金的结构进行了研究,获得了强度曲线、结构因子、双体分布函数和原子间最近邻距离.结果表明,Mg₇₀Zn₃₀合金在小Q区间存在强烈的预峰现象.根据预峰的特性,提出了Mg₇₀Zn₃₀熔体的结构模型,即Mg原子位于中心,8个Zn原子位于顶角所形成的简单立方结构模型.该模型以共享顶点的方式相连接,能够满足预峰对Mg—Mg原子间距离的要求.Mg< 关键词： 非晶态 70Zn₃₀合金')" href="#">Mg₇₀Zn₃₀合金 结构因子 预峰     

Ca70Mg30金属玻璃形成过程热力学、 动力学和结构特性转变机理的模拟研究

采用分子动力学方法对Ca₇₀Mg₃₀合金快速凝固玻璃形成过程进行了计算机模拟, 深入分析了液-固玻璃转变过程热力学、 动力学和结构特性的转变机理, 对不同方法所确立的玻璃转变温度之间的关系进行了探讨. 结果表明: 本模拟计算所获得的Ca₇₀Mg₃₀金属玻璃的结构因子和玻璃转变温度均与实验结果符合, 而且二十面体局域结构对Ca₇₀Mg₃₀金属玻璃的形成起决定性作用. 由于周围原子形成的瞬时"笼子效应", 过冷液体动力学特性逐渐偏离Arrhenius规律而满足模态耦合理论的幂指数规律. 动力学玻璃转变温度接近于微观结构玻璃转变温度, 但高于热力学玻璃转变温度; 而且它们与理想动力学玻璃转变温度之间满足Odagaki关系.     

石英玻璃衬底上纤锌矿Mg0.25Zn0.75O薄膜的结构及光学性能

Mg_xZn_1-xO材料是一种新型光电功能材料.采用溶胶凝胶法在石英玻璃上制备了Mg_0.25Zn_0.75O薄膜,理论结合实验研究了Mg_0.25Zn_0.75O薄膜的结构和光学性能.研究表明,石英玻璃衬底上Mg_0.25Zn_0.75O薄膜呈六方纤锌矿结构,薄膜均匀,平均粒径约为20nm.吸收光谱表明吸收带边始于3 关键词： 0.25Zn_0.75O薄膜')" href="#">Mg_0.25Zn_0.75O薄膜 溶胶凝胶法 石英玻璃衬底 紫外发光     

A simulation study of rapid solidification and crystal configuration of Cu70Ni30 alloy

A molecular dynamics (MD) simulation study has been performed for the rapid solidification of Cu₇₀Ni₃₀ adopting the quantum Sutton-Chen many-body potentials. By analyzing the bond-types and the relation of atomic average energy versus temperature, it was demonstrated that as cooling rate being 2×10¹² K/s, the Cu₇₀Ni₃₀ formed fcc crystal structures and freezing point was found. In addition, having analyzed the transformation of microstructures and the detail of crystal growth by using atomic trace and visual method, not only could the formation of binary disordered solid solution be showed, but also the solidification of liquid metals and the crystal growth processes could be, further understood.     

钴和铁熔体短程序的分子动力学模拟

通过分子动力学模拟研究了金属钴和铁熔体从普通液态到过冷液态普通微观结构的性质.所计算两体分布函数与可获得的实验结果基本一致,从普通液态到过冷液态的局域结构中的原子配位数为11和12的分布几率随着温度的降低而变小,而原子的配位数大于12的分布几率反而增加,角分布函数位于55.有一个明显的峰,位于110°有一个宽展的峰,位于150°有一个肩膀,表明金属钴和铁熔体的微观局域结构要比规则的二十面体团簇的结构复杂得多.我们的模拟结果表明金属熔体中的二十面体短程序随着温度的降低而增加,并在过冷液态中而占优势.     

Al89La6Ni5非晶合金的第一性原理分子动力学模拟

采用第一性原理分子动力学（AIMD）方法模拟 Al89La6Ni5 合金的退火过程,结合双体相关函数和配位多面体（团簇）分布分析了体系短程有序结构随温度的演化. 结构分析表明,非晶态 Al89La6Ni5 原子短程有序结构近似密堆排列;在非晶形成过程中,Al 原子周围短程有序结构几乎没有发生变化,而 La 和 Ni 原子周围环境发生明显改变,由此推测,La 原子的加入改变了 Ni 原子周围的短程有序结构,因而增加了 Al-La-Ni 体系的非晶形成能力;Al 原子和 Ni 原子间存在 Al-Ni 共价键作用,电子态密度的计算说明,费米面附近 Al-p 和 Ni-d 之间电子的相互作用是 Al-Ni 原子间形成局域共价键的原因.     

Al89La6Ni5非晶合金的第一性原理分子动力学模拟

采用第一性原理分子动力学（ AIMD）方法模拟 Al89 La6 Ni5合金的退火过程,结合双体相关函数和配位多面体（团簇）分布分析了体系短程有序结构随温度的演化。结构分析表明,非晶态 Al89 La6 Ni5原子短程有序结构近似密堆排列;在非晶形成过程中,Al 原子周围短程有序结构几乎没有发生变化,而 La 和 Ni原子周围环境发生明显改变,由此推测,La 原子的加入改变了 Ni 原子周围的短程有序结构,因而增加了Al－La－Ni 体系的非晶形成能力;Al 原子和Ni原子间存在Al－Ni共价键作用,电子态密度的计算说明,费米面附近Al－p和Ni－d 之间电子的相互作用是Al－Ni原子间形成局域共价键的原因。     

Synthesis of (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 powder and sintered ferrites by high energy ball-milling process

(Mg_0.476Mn_0.448Zn_0.007)(Fe_1.997Ti_0.002)O₄ nanocrystalline powder prepared by high energy ball-milling process were consolidated by microwave and conventional sintering processes. Phases, microstructure and magnetic properties of the ferrites prepared by different processes were investigated. The (Mg_0.476Mn_0.448Zn_0.007)(Fe_1.997Ti_0.002)O₄ nanocrystalline powder could be prepared by high energy ball-milling process of raw Fe₃O₄, MnO₂, ZnO, TiO₂ and MgO powders. Prefired and microwave sintered ferrites could achieve the maximum density (4.86 g/cm⁻³), the average grain size (15 μm) was larger than that (10 μm) prepared by prefired and conventionally sintered ferrites with pure ferrite phase, and the saturation magnetization (66.77 emu/g) was lower than that of prefired and conventionally sintered ferrites (88.25 emu/g), the remanent magnetization (0.7367 emu/g) was higher than that of prefired and conventionally sintered ferrites (0.0731 emu/g). Although the microwave sintering process could increase the density of ferrites, the saturation magnetization of ferrites was decreased and the remanent magnetization of ferrites was also increased.     

Fe_50Cu_50合金熔体相分离过程的分子动力学模拟

基于镶嵌原子势,采用分子动力学模拟的方法探讨了Fe50Cu50合金熔体在1823 K下液-液相分离过程.结果发现:熔体中同类原子配位数随弛豫时间的延长逐渐增大,而异类原子配位数逐渐减少;由BhatiaThornton结构因子SCC(q)获得的相关长度随时间的变化也呈现出明显的递增趋势,表明该合金熔体在该温度下发生了液—液相分离.原子轨迹的可视化显示结果发现,相分离的初期,体系呈明显的网络状组织,随时间的延长,异类原子逐渐分离,最终形成富Fe和富Cu的相分离组织,符合调幅分解特征.与Fe75Cu25合金熔体的相分离过程对比发现,Fe与Cu原子数目相差越小,相分离行为越剧烈,形成稳定分层结构所需的时间越短.以上研究从原子尺度上表征了金属熔体的相分离过程.     

衬底温度对PLD法生长的Mg0.05Zn0.95O薄膜结构和发光特性的影响

用脉冲激光沉积(PLD)法在不同温度的Si(111)衬底上成功制备了c轴择优取向的Mg_005Zn_095O薄膜.通过X射线衍射(XRD)和光致发光谱(PL)研究了衬底温度对Mg_005Zn_095O薄膜结构和发光特性的影响,探讨了薄膜的结晶质量与发光特性之间的关系.结果表明,在衬底温度为450℃时生长的Mg_005Zn_095O薄膜具有很好的c轴取向和较强的光致发光峰.室温下分别用激发波长为240,300和325nm的氙灯作为激发光源得到不同样品的PL谱,分析表明紫外发光峰和紫峰来源于自由激子的复合辐射且发光强度与薄膜的结晶质量密切相关,蓝绿发光峰与氧空位有关.此外,探讨了衬底温度影响紫外光致发光峰红移和蓝移的可能机理. 关键词： 005Zn_095O薄膜')" href="#">Mg_005Zn_095O薄膜 PLD 衬底温度 光致发光     

Phase transition in Pd40Ni10Cu30P20 bulk metallic glass under HP & HT

The phase transitions in Pd₄₀Ni₁₀Cu₃₀P₂₀ bulk metallic glass (BMG) have been studied under high pressure and high temperature (HP & HT) by X-ray diffaction measurements with synchrotron radiation source. We found that the BMG underwent a phase transitions of amorphous-crystalline-amorphous at 10 GPa upon heating. The parallel experiments were carried out at 7 GPa, while we did not observe the amorphous-crystalline-amorphous transitions by increasing temperature. Quenching the melted BMG at 7 GPa, it was found that the phase crystallized from the melt differed from the primary phase crystallized from the starting amorphous solid upon heating suggesting there existed a distinct mechanism in two cases.     

TiO2/ZnO纳米薄膜界面热导率的分子动力学模拟

采用平衡分子动力学方法及Buckingham势研究了金红石型TiO₂薄膜与闪锌矿型ZnO薄膜构筑的纳米薄膜界面沿晶面[0001](z轴方向)的热导率.通过优化分子模拟初始条件中的截断半径r_c和时间步后,计算并分析了平衡温度、薄膜厚度、薄膜截面大小对热导率的影响.研究表明,薄膜热导率受薄膜温度和厚度的影响很大,当温度由300 K升高600 K时,薄膜的热导率逐渐减小;当薄膜厚度由1.8 nm增大到5 nm时,热导率会逐渐增大;并在此基础 关键词： 热导率 分子动力学 2/ZnO纳米薄膜界面')" href="#">TiO₂/ZnO纳米薄膜界面 数值模拟     

XAFS和XRD研究高能球磨对Fe70Cu30合金结构的影响

利用XRD和XAFS方法研究机械合金化Fe₇₀Cu₃₀二元金属合金随球磨时间的结构变化.XRD结果表明，球磨2 h后，部分金属Fe与Cu生成Fe-Cu合金；球磨20h后，金属Fe与Cu已完全合金化生成Fe-Cu合金，并只在2θ=44°处出现一个宽化的弱衍射峰，认为是在球磨20h后的Fe₇₀Cu₃₀合金中共存着fcc和bcc结构的Fe-Cu合金相.XAFS结果进一步表明，在球磨的初始阶段(2h)，fcc结构的Cu颗粒的晶 关键词： XAFS XRD 70Cu₃₀合金')" href="#">Fe₇₀Cu₃₀合金 机械合金化     

A simulation study of rapid solidification and crystal configuration of Cu<Subscript>70</Subscript>Ni<Subscript>30</Subscript> alloy

A molecular dynamics (MD) simulation study has been performed for the rapid solidification of Cu₇₀Ni₃₀ adopting the quantum Sutton-Chen many-body potentials. By analyzing the bond-types and the relation of atomic average energy versus temperature, it was demonstrated that as cooling rate being 2×10¹² K/s, the Cu₇₀Ni₃₀ formed fcc crystal structures and freezing point was found. In addition, having analyzed the transformation of microstructures and the detail of crystal growth by using atomic trace and visual method, not only could the formation of binary disordered solid solution be showed, but also the solidification of liquid metals and the crystal growth processes could be, further understood.     

分子动力学模拟不同组分下CaO-Al2O3-SiO2系玻璃微观结构的转变

采用分子动力学模拟的方法研究了CaO-Al₂O₃-SiO₂系玻璃的微观结构，发现Ca/Al=1/2时CaO-Al₂O₃-SiO₂系玻璃(网硅酸盐体系)并不像传统理论认为的那样是一个完整的三维网络，而是存在一定量的非桥氧，从而从理论上进一步证实了Stebins等人的实验结果.同时也发现不同的Ca/Al比对Si和Al键接方式产生重要影响，在Ca/Al>1/2时，Al比Si容易成为网络的中间体，其首先插入网络体中间；在Ca/Al<1/2时，Si比Al容易成为网络中间体.虽然在能量上Al—O—Si占有扰势，但当Ca/Al从大于1/2变化到小于1/2时，仍有部分Al—O—Si转变成Al—O—Al和Si—O—Si，丰富了Al自回避规则的内容. 关键词： 2O₃-SiO₂')" href="#">CaO-Al₂O₃-SiO₂ 玻璃 微观结构 分子动力学     

Green emitting long lasting phosphorescence (LLP) properties of Mg2SnO4:Mn phosphor

A novel long-lasting phosphorescence phosphor, Mn²⁺-activated Mg₂SnO₄, has been synthesized and its optical properties have been investigated. The Mg₂SnO₄:Mn²⁺ emits green light with high luminance, upon UV irradiation, centered at 499 nm from the spin forbidden transitions of the d-electrons in Mn²⁺ ions. The CIE chromaticity coordinates of the Mg₂SnO₄:Mn²⁺ phosphor are x=0.0875 and y=0.6083 under 254 nm UV excitation. The phosphorescence can be observed by the naked eyes (0.32 mcd/m²) in the dark clearly for over 5 h after the 5 min UV irradiation. Thermoluminescence has been studied and the mechanism of the long-lasting phosphorescence has been discussed.     

Mössbauer study of local environment effects in the ordered Fe70Al30 Invar alloy: Temperature dependence of isomer shift in the spin-glass phase

The systematic studies of the magnetic hyperfine field distribution for ⁵⁷Fe in the spin-glass (SG) phase of the ordered Fe₇₀Al₃₀ Invar alloy have been performed using Mössbauer spectroscopy technique in the temperature range from 5 to 80 K. Particular emphasis has been placed on the low-field component of the distribution, which is considered as corresponding to the Fe sites in the SG magnetic configurations. The main result is the observation of the pronounced temperature dependence of isomer shift for several atomic SG configurations. The temperature behavior of the local electron density is strongly correlated to the Invar properties of the Fe₇₀Al₃₀ alloy. We argue that the observed temperature dependence of the isomer shift due to a local volume effect. The temperature range, for which the pronounced decrease in atomic volume is observed, coincides with the range of the existence of the Invar effect. The influence of the competition between opposite in sign exchange interactions on the Invar properties is discussed.     

内嵌金属富勒烯Tcn和Tcn@C70的理论研究

系统地研究了内嵌金属富勒烯Tc_n和Tc_n@C₇₀的平衡态结构、电子和磁性性质．研究表明C₇₀能够内嵌Tc_n团簇(n≤9)．除了Tc₂团簇,当n≤5时,形成内嵌金属富勒烯Tc_n@C₇₀是放热的过程,而当n>5时,这种过程是吸热的．在内嵌过程中,Tc_n团簇的构型和电子结构都发生了相当大的变化．与单独的Tc_n团簇相比,Tc_n@C₇₀的总磁矩明显地降低．对体系的轨道分布,Hirshfeld分布和态密度进行了分析发现,在内嵌金属富勒烯体系里,电子可以通过Tc-C的有效杂化从Tc_n团簇向碳笼转移,从而使得体系的整体磁性降低．     

Photoemission intensity oscillations in the valence bands of C70 film

We have measured and analyzed the photoemission spectra (PES) of a C₇₀ film in the photon energy region from 13.4 eV to 98.4 eV. The photoelectron intensities of two C 2p π-derived features (denoted by A and B) oscillate regularly in the whole energy region with some fine structures below ∼30 eV. To obtain the detailed information of the oscillations, we have developed a sophisticated but practical procedure for intensity calculation. The procedure consists of two core concepts. The first is ascribing the PES features to their corresponding molecular orbitals with the help of density functional calculations. The second is a background subtraction algorithm. With this procedure, we obtained the oscillating behavior for individual features (A and B), which is by and large consistent with the predictions based on the spherical symmetric approximation although C₇₀ has the ellipsoidal shape. Owing to the solid state effect, the oscillating amplitudes of the A/B intensity ratios are smaller than those of gas phase C₇₀, but an orbital shift reported recently was not observed on our sample. The oscillating curve of a deeper feature, which consists of both σ and π states, are also reported.     

Anisotropic domain-wall dynamics in proton-irradiated KH2PO4

KH₂PO₄ single crystals have been studied by employing complex impedance measurements in view of the domain freezing effect. As a result, distinct behaviors of the anisotropic domain-wall dynamics in the activation energy of domain freezing and the Vogel–Fulcher temperature before and after proton irradiation have been identified in the anisotropic crystal structure.