International Center for New-Structured Materials and Laboratory of New-Structured Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, People's Republic of China.
Proc Natl Acad Sci U S A. 2013 Jun 18;110(25):10068-72. doi: 10.1073/pnas.1307967110. Epub 2013 Jun 3.
When a material is heated, generally, it dilates. Here, we find a general trend that the average distance between a center atom and atoms in the first nearest-neighbor shell contracts for several metallic melts upon heating. Using synchrotron X-ray diffraction technique and molecular dynamics simulations, we elucidate that this anomaly is caused by the redistribution of polyhedral clusters affected by temperature. In metallic melts, the high-coordinated polyhedra are inclined to evolve into low-coordinated ones with increasing temperature. As the coordination number decreases, the average atomic distance between a center atom and atoms in the first shell of polyhedral clusters is reduced. This phenomenon is a ubiquitous feature for metallic melts consisting of various-sized polyhedra. This finding sheds light on the understanding of atomic structures and thermal behavior of disordered materials and will trigger more experimental and theoretical studies of liquids, amorphous alloys, glasses, and casting temperature effect on solidification process of crystalline materials.
当物质被加热时，通常会发生膨胀。在这里，我们发现一个普遍趋势，即几种金属熔体在加热时，中心原子与第一近邻壳层原子之间的平均距离会收缩。我们使用同步加速器 X 射线衍射技术和分子动力学模拟，阐明了这种异常是由温度影响的多面体团簇的再分配引起的。在金属熔体中，随着温度的升高，高配位数的多面体倾向于演变成低配位数的多面体。随着配位数的降低，中心原子与多面体第一壳层原子之间的平均原子距离减小。这种现象是由各种尺寸多面体组成的金属熔体的普遍特征。这一发现有助于理解无序材料的原子结构和热行为，并将引发更多关于液体、非晶合金、玻璃以及铸造温度对晶体材料凝固过程影响的实验和理论研究。
