Entropy difference between the face-centred cubic and hexagonal close-packed crystal structures
Entropy difference between the face-centred cubic and hexagonal close-packed crystal structures
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DOI：
10.1038/385141a0
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发表时间：
1997-01-09
期刊：
影响因子：
64.8
通讯作者：
Woodcock, LV
中科院分区：
文献类型：
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作者：
Woodcock, LV
球体可以堆叠成两个紧密堆积的晶体排列，面心立方（f.c.c.）和六方密堆积（h. c. p.），它们具有相同的密堆积体积和非常相似的状态方程（2）。但它们的结构不同，这意味着它们可能具有不同的热力学性质和稳定性。发现两种结构之间的自由能差异一直是许多理论（3，4）和计算（5-7）努力的目标，但没有结论性的解决方案，在这里，我报告说，在这些填料的单占据单元模型（8）内的机械不稳定点附近可以检测到压力-体积（P-V）行为的显著差异，该模型提供了两种结构之间的精确的热力学可逆路径，并且可以对P-V等温线进行积分以获得吉布斯自由能差。我发现联邦通信委员会。相更稳定约0.005RT每摩尔（其中R是通用气体常数）;由于焓差可以忽略不计，这意味着熵差在所有温度下都是0.005R的数量级。
SPHERES can be stacked into two close-packed crystalline arrangements, face-centred cubic (f.c.c.) and hexagonal closed-packed (h.c.p.), which have identical close-packed volumes' and very similar equations of state(2). But they are structurally distinct, implying that they might have different thermodynamic properties and stabilities. Finding a difference in free energy between the two structures has been the objective of much theoretical(3,4) and computational(5-7) effort, but without a conclusive resolution, Here I report that a significant difference in the pressure-volume (P-V) behaviour can be detected in the vicinity of a mechanical instability point within a single-occupancy cell model(8) of these packings, This model provides an exact thermodynamically reversible path between the two structures, and sa, the P-V isotherms can be integrated to obtain the Gibbs free-energy difference. I find that the f.c.c. phase is more stable by around 0.005RT per mol (where R is the universal gas constant); as the enthalpy difference is negligible, this implies that the entropy difference is of the order of 0.005R for all temperatures up to the melting point.