Abstract

Using density-functional theory based simulations, we study how initially disconnected zinc phosphate molecules respond to different externally imposed deformations. Hybridization changes are observed in all cases, in which the coordination of zinc atoms changes irreversibly from tetrahedral to seesaw and square pyramidal, whereby the system stiffens substantially. The point at which stiff networks are formed does not only depend on the hydrostatic pressure. Stress anisotropy generally reduces the required hydrostatic network formation pressure. Moreover, networks obtained under isotropic deformations turn out stiffer, elastically more isotropic, and lower in energy after decompression than those produced under anisotropic stresses. We also find that the observed stress-memory effects are encoded to a significant degree in the arrangement of atoms in the second neighbor shell of the zinc atoms. These findings refine previously formulated conjectures of pressure-assisted cross-linking in zinc phosphate-based anti-wear films.

Graphical Abstract

中文翻译：

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应力各向异性严重影响磷酸锌网络的形成

摘要

使用基于密度泛函理论的模拟，我们研究最初断开连接的磷酸锌分子如何响应不同的外部施加变形。在所有情况下都观察到杂化变化，其中锌原子的配位不可逆地从四面体变为跷跷板和四方锥体，从而使系统显着变硬。刚性网络的形成点不仅取决于静水压力。应力各向异性通常会降低所需的静水网络形成压力。此外，与在各向异性应力下产生的网络相比，在各向同性变形下获得的网络在减压后变得更硬、弹性更各向同性且能量更低。我们还发现观察到的应力记忆效应在锌原子的第二个相邻壳层中的原子排列中在很大程度上被编码。这些发现改进了先前提出的关于磷酸锌基抗磨膜中压力辅助交联的猜想。

图形概要