非平衡定态相图新概念及其应用——激活低压金刚石气相生长热力学

在激活的低压条件下，金刚石气相稳定生长的同时石墨会被腐蚀．这是近二三十年来国际上的一个热力学难题，甚至被认为是“热力学的悖论”．用非平衡热力学耦合理论可以给予很好的解释，并推导出非平衡定态相图的全新概念．在新型相图中金刚石在低压下是稳定相，而石墨被激活成为亚稳相．理论计算与文献报道的大量实验数据定量化地相符     

非平衡定态相图新概念及其应用

在激活的低压条件下，金刚石气相稳定生长的同时石墨会被腐蚀、这是近二三十年来国际上的一个热力学难题，甚至被认为是“热力学的悖论”，用非平衡热力学耦合理论可以给予很好的解释，并推导出非平衡定态相图的全新概念，在新型相图中金刚石在低压下是稳定相，而石墨被激活成为亚稳相，理论计算与文献报道的大量实验数据定量化地相符。     

现代热力学基础简介

从热力学基本定律的现代表达式 (diS≥ 0 ,diS是体系的熵产生 )能直接预测同时发生的反应有发生反应耦合 [diS1<0 ,diS2 >0和diS1 diS2 ≥ 0 ;diS1和diS2 是反应的熵产生 ]的可能 ,但是长期以来无法得到定量证明 .在激活低压气相生长金刚石的热力学研究中 ,发现该体系就是反应耦合的定量化例证 ,相应地得到了一个非平衡零耗散热力学 [diS1<0 ,diS2 >0和diS1 diS2 =0 ]的全新热力学分支领域 .非平衡定态相图的计算就是该领域的重要结果 ,并与大量的金刚石气相生长实验相符 .非平衡零耗散体系是在外界强制条件下的一种定态体系 ,强制条件减弱为零时就成为平衡体系 .现代热力学对开放体系相关的近代高新科技领域有重要意义 .     

电子助进热丝化学汽相沉积金刚石薄膜

以CH₄和H₂为源反应气体，利用电子助进热丝化学汽相沉积（CVD）技术，在Si（100）晶面衬底上成功地得到了织构生长的金刚石薄膜．用扫描电子显微镜、Raman光谱、X射线衍射等多种技术对薄膜的形貌、成分、晶态等特性进行了分析，得到了在热丝CVD实验条件下织构生长金刚石薄膜的最佳工艺条件． 关键词：     

氩气掺入对类金刚石沉积过程的影响

在电子助进化学气相沉积(EACVD)类金刚石薄膜中,使用和比较CH₄/H₂与CH₄/H₂/Ar两种体系,用静电探针测量这两种体系的电子温度、电子密度,结果表明,在CH₄/H₂/Ar体系中,电子密度较高,使成膜的速率增加。 关键词：     

B2O3添加宝石级金刚石单晶的生长特性

利用温度梯度法, 在5.3-5.7 GPa压力、1200-1600 ℃的温度条件下, 将B₂O₃粉添加到FeNiMnCo+C合成体系内, 进行B₂O₃添加宝石级金刚石单晶的合成. 研究得到了FeNiMnCo触媒生长B₂O₃添加宝石级金刚石单晶的相图分布规律. 结果表明B₂O₃添加会使晶体生长的“V”形区上移和低温六面体单晶生长区间变宽. 通过晶体生长实验, 研究合成了不同形貌的B₂O₃添加宝石级金刚石单晶. 研究同时证实, B₂O₃的过量添加会对宝石级金刚石单晶生长带来不利影响. 当B₂O₃的添加量高于约3 wt‰、生长时间超过20 h时, 很难实现优质B₂O₃添加宝石级金刚石单晶的生长. 但B₂O₃的适量添加(不超过1 wt‰), 有助于提高低温板状六面体宝石级金刚石单晶的成品率. 通过对晶体生长速度的研究发现, B₂O₃的添加使得优质晶体的生长速度明显降低, 随着晶体生长时间的延长, B₂O₃添加剂对晶体生长的抑制作用会越发明显. 扫描电镜测试结果表明, 合成体系内B₂O₃添加剂的引入, 导致晶体表面的平整度明显下降.     

评<非平衡定态相图--人造金刚石的低压气相生长热力学>一书

<非平衡定态相图--人造金刚石的低压气相生长热力学>一书于2000年3月由科学出版社出版,这是复旦大学王季陶教授得到国家自然科学基金委员会优秀研究成果专著出版基金资助的出版物.书名中有两个关键词引人注目.其一是广为人知的"金刚石",自古以来它以其璀璨夺目而一直是人们心目中的宝石之王;到近代人们又认识到它是具有最高硬度和弹性模量的超硬材料,但它的其他优异性能和潜在的高技术应用还远超出一般人所知的范围.     

钚氧化物中氢行为的第一性原理研究

通过第一性原理计算和原子级热力学方法，系统研究H、H₂在PuO₂和α-Pu₂O₃中的吸附、扩散和溶解行为.研究发现：氢的上述行为均是吸热过程，但在α-Pu₂O₃与PuO₂中有显著不同：在α-Pu₂O₃中H可自发聚合成H₂，但在PuO₂中H难再聚合；在α-Pu₂O₃中H、H₂均能扩散，通常H会聚合成H₂再扩散，在PuO₂中H₂解离后才能扩散，且PuO₂中H沿高势能面的扩散比α-Pu₂O₃中H₂扩散更容易；在氢压、温度驱动下，氢在α-Pu₂O₃中存在H₂溶解到H+H₂混合溶解机制的转变，平衡气压P_H2远小于H在PuO₂中溶解的情况.基于此，给出PuO₂和α-Pu₂O₃中氢行为的微观图像和PuO₂的阻氢微观机制：PuO₂表面限制H₂解离、渗透，PuO₂块体限制H的溶解，但不阻止H扩散.结合钚氧化层表面氢行为研究获得了钚氢化孕育期的微观机制，为孕育期全过程理论建模提供依据.     

CH4或CH4+Ar介质阻挡放电中的离子能量和类金刚石膜制备

实验上，利用纯CH₄及CH₄+Ar在几百帕量级气压下的介质阻挡放电 制备类金刚石膜，研究了气压p与放电间隙d乘积(pd值)以及Ar的体积百分比R_Ar 对膜硬度的影响.理论上，从离子与气体分子的双体碰撞出发，利用较高折合电场强度E/n( 电场强度与粒子数密度之比)下离子及中性粒子速度分布的双温模型、离子在其他气体中运 动时遵守的朗之万方程及离子在混合气体中运动时遵守的布兰克法则，对CH⁺4和Ar⁺离子能量进行了分析.结果表明：1)CH₄介质阻挡 放电中，pd值由1.862×10³Pa mm降低至2.66×10²Pa mm时，CH+₄能量由5.4eV增加到163eV，类金刚石膜硬度由2.1GPa提高到17.6GPa ; 2) 保持总气压p=100Pa,放电间距d=5mm不变，在CH₄中加入Ar气，当R_Ar 由20％增加至83%时，CH⁺₄的能量由69eV增加到92eV,而Ar＋能量由93eV降低至72eV.虽然CH⁺₄能量增加有助于提高 沉积膜硬度，但当R_Ar大于67%，高强度Ar⁺轰击会导致膜表面石墨 化，膜硬度降低.为了验证离子能量理论模型的正确性，实验测量了H₂介质阻挡 放电中离子能量，测量结果与理论计算之间最大相对误差为16%. 关键词： 离子能量 介质阻挡放电 类金刚石膜     

H2对Ar稀释SiH4等离子体CVD制备多晶硅薄膜的影响

以SiH₄，Ar和H₂为反应气体，采用射频等离子体化学气相沉积方法在300℃下制备了低温多晶Si薄膜.实验发现，反应气体中H₂的比例是影响薄膜结晶质量的重要因素，在适量的H₂比例下制备的多晶Si薄膜具有结晶相体积分数高，氢含量低，生长速率快、抗杂质污染等特性. 关键词： 低温多晶Si薄膜 等离子体CVD 4')" href="#">Ar稀释SiH₄ 2比例')" href="#">H₂比例     

Critical evaluation and thermodynamic modeling of the Mn–Cr–O system for the oxidation of SOFC interconnect

A complete critical evaluation and thermodynamic modeling of the phase diagrams and thermodynamic properties of the Mn–Cr–O system at 1 bar total pressure are presented. Optimized equations for the thermodynamic properties of all phases are obtained, which reproduce all available and reliable thermodynamic and phase equilibrium data within experimental error limits from 25 °C to above the liquidus temperatures at all compositions and oxygen partial pressures. As results of optimization, the Gibbs energy function of MnCr₂O₄ is for the first time properly estimated and the discrepancies of the phase diagram experiments of the Mn–Cr–O system are resolved. In particular, unexplored phase diagrams and thermodynamic properties of the Mn–Cr–O system of importance for the oxidation of SOFC interconnect are predicted on the basis of the optimized model parameters. The database of the model parameters can be used along with software for Gibbs energy minimization in order to calculate any type of phase diagram sections and thermodynamic properties.     

A thermodynamic lattice theory on melting curve and eutectic point of binary alloys. Application to fcc and bcc structure

A thermodynamic lattice theory has been developed for determination of the melting curves and eutectic points of binary alloys. Analytical expressions for the melting curves of binary alloys composed of constituent elements with the same structure have been derived from expressions for the ratio of root mean square fluctuation in atomic positions on the equilibrium lattice positions and the nearest neighbor distance. This melting curve provides information on Lindemann’s melting temperatures of binary alloys with respect to any proportion of constituent elements, as well as on their eutectic points. The theory has been applied to fcc and bcc structure. Numerical results for some binary alloys provide a good correspondence between the calculated and experimental phase diagrams, where the calculated results for Cu_1−x Ni _x agree well with the measured ones, and those for the other alloys are found to be in a reasonable agreement with experiment.     

Thermal transport property of Ge34 and d-Ge investigated by molecular dynamics and the Slack’s equation

In this study,we evaluate the values of lattice thermal conductivity κ L of type II Ge clathrate (Ge 34) and diamond phase Ge crystal (d-Ge) with the equilibrium molecular dynamics (EMD) method and the Slack's equation.The key parameters of the Slack's equation are derived from the thermodynamic properties obtained from the lattice dynamics (LD) calculations.The empirical Tersoff's potential is used in both EMD and LD simulations.The thermal conductivities of d-Ge calculated by both methods are in accordance with the experimental values.The predictions of the Slack's equation are consistent with the EMD results above 250 K for both Ge34 and d-Ge.In a temperature range of 200-1000 K,the κ L value of d-Ge is about several times larger than that of Ge 34.     

Microcanonical ensemble study of a gas column under gravity

The study of a classical ideal gas column of finite height H in a uniform gravitational field g is made by the microcanonical ensemble at energy E. The primary functions of this ensemble, the phase volume and the density of states, are derived. Related statistical quantities, such as the entropy, the temperature and the heat capacity, are also reported. The equivalence in the thermodynamic limit between the calculated microcanonical expressions and those obtained from the canonical ensemble is shown numerically. The expression for the temperature is used to analyze the temperature change when the gas is permitted to expand into an evacuated region increasing the height of the column from H ₁ to H ₂. The microcanonical single-particle momentum and height distributions are also reported.     

Phase diagrams of atomic ordering in alloys with the superstructures L12 and L1o

For different values of the atomic interaction in the first and second coordination spheres, phase diagrams of atomic ordering in alloys with an fcc lattice are calculated by the Kikuchi method in the tetrahedron + triangle approximation. In addition to order-disorder transitions, the equilibrium of two ordered phases with the superstructures L1₂ and L1_o and the form of the diagram close to three-phase equilibrium are considered. The calculated diagrams and order-disorder transition temperatures are compared with the analogous results obtained in the tetrahedron approximation. In view of the lack of considerable discrepancy in the results, it may be concluded that the approximation of the entropy of the alloy model in the two approaches is sufficiently good. Hence, the significant difference between the phase diagrams calculated in the present work and the phase diagrams of real alloys is mainly due to the different types of atomic interaction in these alloys.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 13–17, March, 1979.     

Studying the effect of hydrogen on diamond growth by adding C10H10Fe under high pressures and high temperatures

In this paper, hydrogen-doped industrial diamonds and gem diamonds were synthesized in the Fe–Ni–C system with C₁₀H₁₀Fe additive, high pressures and high temperatures range of 5.2–6.2?GPa and 1250–1460°C. Experimental results indicate similar effect of hydrogen on these two types of diamonds: with the increasing content of C₁₀H₁₀Fe added in diamond growth environment, temperature is a crucial factor that sensitively affects the hydrogen-doped diamond crystallization. The temperature region for high-quality diamond growth becomes higher and the morphology of diamond crystal changes from cube-octahedral to octahedral. The defects on the {100} surfaces of diamond are more than those on the {111} surfaces. Fourier transform infrared spectroscopy (FTIR) results indicate that the hydrogen atoms enter into the diamond crystal lattice from {100} faces more easily. Most interestingly, under low temperature, nitrogen atoms can also easily enter into the diamond crystal lattice from {100} faces cooperated with hydrogen atoms.     

Theoretical pressure-temperature phase diagram for [N(CH3)4]2CuCl4

The pressure-temperature phase diagram for a [N(CH₃)₄]₂CuCl₄ crystal has been theoretically constructed using the phenomenological approach developed earlier. The relationships for the thermodynamic potentials of different phases and the boundaries between these phases are derived. The theoretical and experimental diagrams are in reasonable agreement. The approximations and assumptions made in the construction of the diagrams are discussed.     

OES study of the gas phase during diamond films deposition in high power DC arc plasma jet CVD system

This paper used optical emission spectroscopy (OES) to study the gas phase in high power DC arc plasma jet chemical vapour deposition (CVD) during diamond films growth processes. The results show that all the deposition parameters (methane concentration, substrate temperature, gas flow rate and ratio of H₂/Ar) could strongly influence the gas phase. C₂ is found to be the most sensitive radical to deposition parameters among the radicals in gas phase. Spatially resolved OES implies that a relative high concentration of atomic H exists near the substrate surface, which is beneficial for diamond film growth. The relatively high concentrations of C₂ and CH are correlated with high deposition rate of diamond. In our high deposition rate system, C₂ is presumed to be the main growth radical, and CH is also believed to contribute the diamond deposition.     

In-situ combined X-ray diffraction and electrical resistance measurements at high pressures and temperatures in diamond anvil cells

A method of simultaneous X-ray diffraction and electrical resistance measurements of materials in a diamond anvil cell has been developed. The experimental arrangement for the electrical measurements uses a gasket as a part of the electrode scheme. Application of the new methodology is demonstrated on the examples of the study of high-pressure high-temperature behavior of Pr and Fe–Ni alloys. Simultaneously obtained diffraction and resistance data provide the different, from earlier studies, interpretations of the topology of the dhcp–fcc phase transition in the phase diagram of Pr. Namely, the shape of a hysteretic region is mostly defined by kinetics of the dhcp phase growth rather than by thermodynamic driving force at the fcc to dhcp phase transformation. The results of combined X-ray diffraction and resistance measurements of Fe0.₈Ni0.₂ alloy up to 18 GPa and 425 K are reported along with the complementary resistance measurements of Fe0.₉Ni0.₁ alloy.     

First-principles calculation of structural stability,lattice dynamic and thermodynamic properties of BeX (X = S,Se and Te) compounds under high pressure

The phase transitions, lattice dynamical and thermodynamic properties of BeS, BsSe and BeTe at high pressure have been investigated with the density functional theory. The calculated equilibrium structural parameters agree well with the available experimental and theoretical values. The phase transition pressures from the zinc-blende (ZB) to the nickel arsenide (NiAs) phase of these compounds are determined. The calculated phonon dispersion curves of these compounds in ZB phase at zero pressure do not show any anomaly or instability. Dynamically, the ZB phase of BeS, BeSe and BeTe is found to be stable near transition pressures P_T. Within the quasiharmonic approximation, the thermodynamic properties including the thermal expansion coefficient, heat capacity at constant volume, heat capacity at constant pressure and entropy are predicted.