【作者】 刘心笔；

【导师】 谢佑卿；

【作者基本信息】 中南大学 ， 材料物理与化学， 2010， 博士

【摘要】 在合金理论发展的历史进程中,Au-Cu合金系始终是首选的经典的研究对象,晶体学家将其作为合金相晶体结构的研究范例,理论物理学家将它作为合金相电子结构和有序——无序转变的研究范例,热化学家将它作为合金系相图评估和相图理论计算的研究范例。本文应用系统合金科学,选择经典的Au-Cu合金系作为研究对象,在系统研究纯金属Cu、Au基础上,从合金相的原子结构层次和原子的电子结构层次两个层次研究了Au-Cu合金系,确定了合金、组元的能量性质、体积性质、电子结构。研究获得了若干创新性成果,丰富了系统合金科学的内容,为研究合金相有序——无序转变、相图计算和材料设计提供了基础资料。应用系统合金科学中的纯金属理论,研究了纯金属Cu和Au的电子结构、热膨胀系数、单键半径、晶格常数、比热、内能、焓、熵、Gibbs自由能、结合能等性质,计算结果与实验值符合良好。由“部分获得整体”,是系统合金科学中最具特色的方法、最有实用价值的技术,正确选择能量和体积相互作用方程是系统合金科学的首要任务。本文分别以Au-Cu合金系少量无序合金生成热、生成体积实验值为基础和少量化合物的生成热、生成体积实验值为基础的两条研究路线,分别得到合金系中载有特征原子能量性质、体积性质、状态性质的特征原子序列,随后应用纯金属理论,确定特征晶体的价电子结构、结合能、单键半径、晶格常数等信息,这些信息是合金设计和合金相性质计算、有序——无序转变研究以及相图计算的前提。在此基础上,采用双向应证的方法,获得了有价值的成果：确定了能量相互作用方程为第5方程,体积相互作用方程为第6方程；发现了以往实验测量用的无序合金不是完全无序合金,而是具有较大的短程有序度；解释了Au-Cu合金无序化时体积膨胀的原因在于特征原子的体积变化,本质在于随着近邻Au原子数的增加,AiCu的价电子结构中共价电子增加较少,自由电子增加显著,导致单键半径增加,νiCu增加；证明了偏摩尔性质不能真实描述组元的平均性质。应用特征晶体性质相加定律,分别以无序合金和化合物确定的两组特征晶体序列的性质为基础,研究了Au-Cu合金系的无序合金、有序合金和化合物的能量性质、体积性质和电子结构。两条研究路线的研究结论相同：从纯金属生成无序合金、有序合金和化合物都放出热量,从无序→有序转变是放热反应；从纯金属生成无序合金、有序合金和化合物体积都膨胀,相对于Zen定律和Vegard定律是正偏差,从无序→有序转变体积缩小；随着有序度的增加,有序合金的生成热越小,结合能增加,有序合金平均原子体积、晶格常数减小。这也证明了系统合金科学可以从“不同部分获得整体信息”。本文创建了合金相结构新的描述方法——晶体特征原子排列结构,它既反映了合金相特征原子的空间排布,又赋有能量、体积和状态信息。本文根据Johannsson-Linde提出的AuCuⅡ的长周期反相畴“界面”结构模型和Guymont等提出的长周期反相畴“界区”统计结构模型,绘出了对应的晶体特征原子排列结构,分别计算了AuCuⅠ、AuCuⅡ和反相界区(面)的生成热、生成体积、有序度以及AuCuⅠ→AuCuⅡ的转变焓和转变体积。研究结果表明,J-L模型对应的AuCuⅠ→AuCuⅡ转变为放热反应和体积收缩的反应,这与实验表明该反应为吸热反应和体积膨胀反应相矛盾,J-L模型不能真实反映AuCuⅡ的结构。G-F-L模型对应的AuCuⅠ→uCuⅡ转变为吸热反应和体积膨胀的反应,这与实验表明一致。因此,G-F-L模型真实反映AuCuⅡ的结构。更多还原

【Abstract】 In the development history of alloying theory, Au-Cu system is always the classic subject investigated. The crystallogphies target it as an exemplification for studying alloy phase structure; The theoretical physicists choose it as an exemplification for studying electronic structure and transformation of order-disorder; The thermal chemists consider it as an exemplification for evaluating and calculating phase diagram.In this paper, the classic Au-Cu alloy system is chose as object. On the basis of studying pure metals Cu and Au, this alloy system is researched from the two respects of atomic structure level of alloy phase and electronic structure level of atom. Then the energetic properties, volumetric properties and electronic structures of alloys and components are obtained through systematic alloy science. This study produces umpty innovative results, enriches the contents for systematic alloy science and supplies fundamental datum for studying transformation of order-disorder, calculating phase diagram and designing new materials.The electronic structures, coefficients of heat expansion, single bond radii, lattice parameters, specific heats at constant volume, isopiestic specific heats, internal energies, enthalpies, entropies and Gibbs energies of pure metals Cu and Au are studied adopting one-atom theory within systematic alloy science. The calculated results are in good agreement with the experimental datum."Obtaining the whole from the part" is the most idiomatical method in systematic alloy science, the most employable technique and is the principal task of systematic alloy science for choosing the interaction function between energy and volume accurately. This paper obtains, creatively, two characteristic atom sequences, which contain the energetic properties, volumetric properties and state behaviors of characteristic atoms on the basis of experimental heat of formation and volume of formation of a few disordered alloys and experimental heat of formation and volume of formation of a few compounds respectively in Au-Cu system. Then, using the one-atom theory, we determine the information of valence electronic structures, cohesive energies, single bond radii, lattice parameters, etc for characteristic crystals, which are the premise of designing materials, calculating the properties of alloy phases and phase diagrams and studying transformations of order-disorder. On the basis of these, we adopt the method of bidirectional proof and obtain some valuable results:it is determined that the interaction function of energy is equation 5 and the interaction function of volume is equation 6; it is found that the disordered alloys measured by experiment is not full disordered, but have larger degree of short range ordering; it also interpret the question perplexing us chronically of voluminal expansion when disordering in Au-Cu alloy. The reason is that the volume of characteristic atom AiCU increases with increasing the number of nearest neighboring atom Au, essentially, due to both increase of covalent electrons changing smaller and increase of free electrons changing more markedly in valence electronic structure, which is attributed to increase of single bond radius and viCu". Then, it is proved that the partial molar property can’t veritably describe the average properties of components.Using the additivity law of characteristic crystalline properties, the energetic properties, volumetric properties and electronic structures of disordered alloys, ordered alloys and compounds in Au-Cu alloy system are studied from the information of two group of characteristic crystal sequences definited by disordered alloys and compounds. The results of the two studying methods exist small differences, yet the whole conclusions are same:the formations of disordered alloys, ordered alloys and compounds from pure metals are exothermic and their volumes are expansive, which is positive deviation relative to Zen’s Law and Vegard’s Law, and that the transformation of disordered→ordered is exothermic reaction and its volume is contractible. Also, these prove that systematic alloy science can obtain the whole infromation from different parts.It is proposed a new description method of phase structure, i.e., the crystal characteristic atom arranging structure which not only reflects the arrangement of atoms in space, but also contains the information of energies, volumes and states. According to the J-L long period antiphase structure model proposed by Johannsson-Linde and G-F-L model proposed by Guymont-Feutelais-Legendre, we illustrate the corresponding crystal characteristic atom arranging structures respectively. Then the heats of formation, volumes of formation and ordering degree of AuCuⅠ, AuCuⅡand the region (plane) of antiphase, as well as the enthalpy of transition and volume of transition of AuCuⅠ→AuCuⅡare all calculated respectively. The results denote that the transition of AuCuⅠ→AuCuⅡcorresponding to J-L model is an exothermic and volume contractic reaction which is opposite from experimental phenomenon. Therefore, the J-L model can not be used to describe the structure of AuCuⅡ. However, the transition of AuCuⅠ→AuCuⅡcorresponding to G-F-L model is an endothermic and voluminal expansion reaction which is in agreement with the experimental phenomenon. Thus, the G-F-L model reflects the structure of AuCuⅡfactually.更多还原