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首页> 外文期刊>The Journal of Chemical Physics >Transformation of topologically close-packed beta-W to body-centered cubic alpha-W: Comparison of experiments and computations
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Transformation of topologically close-packed beta-W to body-centered cubic alpha-W: Comparison of experiments and computations

机译：将拓扑封闭式β-W转换为身体中心的立方α-W：实验和计算的比较

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摘要

The enthalpy and activation energy for the transformation of the metastable form of tungsten, beta-W, which has the topologically close-packed A15 structure (space group Pm<(3)overbar>n), to equilibrium alpha-W, which is body-centered cubic (A2, space group Im (3) over barm), was measured using differential scanning calorimetry. The beta-W films were 1 mu m-thick and were prepared by sputter deposition in argon with a small amount of nitrogen. The transformation enthalpy was measured as -8.3 +/- 0.4 kJ/mol (-86 +/- 4 meV/atom) and the transformation activation energy as 2.2 +/- 0.1 eV. The measured enthalpy was found to agree well with the difference in energies of alpha and beta tungsten computed using density functional theory, which gave a value of -82 meV/atom for the transformation enthalpy. A calculated concerted transformation mechanism with a barrier of 0.4 eV/atom, in which all the atoms in an A15 unit cell transform into A2, was found to be inconsistent with the experimentally measured activation energy for any critical nucleus larger than two A2 unit cells. Larger calculations of eight A15 unit cells spontaneously relax to a mechanism in which part of the supercell first transforms from A15 to A2, creating a phase boundary, before the remaining A15 transforms into the A2 phase. Both calculations indicate that a nucleation and growth mechanism is favored over a concerted transformation. More consistent with the experimental activation energy was that of a calculated local transformation mechanism at the A15-A2 phase boundary, computed as 1.7 eV using molecular dynamics simulations. This calculated phase transformation mechanism involves collective rearrangements of W atoms in the disordered interface separating the A15 and A2 phases. Published by AIP Publishing.
机译：用于转化钨，β-W的焓和活化能量，其具有拓扑封闭的A15结构（空间群PM <（3）延伸率> n），达到α-W，这是体 - 使用差示扫描量热法测量Cenfic（A2，Space Group IM（3））。 β-W薄膜是1μm厚的，并且通过氨基中的溅射沉积制备，少量氮气。将转化焓测量为-8.3 +/- 0.4kJ / mol（-86 +/- 4mev /原子），转化激活能量为2.2 +/- 0.1eV。发现测量的焓与使用密度泛函理论计算的α和β钨的能量差异很好，这给了转化焓为-82mev /原子的值。具有0.4eV /原子的屏障的计算的齐齐的转化机制，其中A15单位细胞转化中的所有原子变为A2，发现与大于两个A2单元细胞的任何关键核的实验测量的活化能量不一致。较大的八个A15单元细胞的计算自发地放松到一个机构，在剩余A15在剩余A15变换到A2相位之前，将超级电池的一部分从A15变换为25到A2。两种计算表明核心和生长机制在一致转化中受到青睐。更符合实验激活能量的是A15-A2相边界处计算出的局部变换机制，使用分子动力学模拟计算为1.7eV。该计算的相变制机制涉及在分离A15和A2阶段的无序界面中的W原子的集体重排。通过AIP发布发布。

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