In this paper, density functional theory simulations were conducted to investigate the structural adaptation of sodium borates xNa2O·(100-x)B2O3 (x = 25, 33, 50, and 60 mol %) during the compression/decompression between 0 and 10 GPa. The sodium borates are confined between two Fe2O3 substrates and undergo the compression by reducing the gap between the two surfaces. The results reveal the borate response to the load through a two-stage transformation: rearrangement at low pressure and polymerization at high pressure. The pressure required to initiate the polymerization depends directly on the portion of fourfold-coordinated ([4]B) boron in the sodium borates. We found that the polymerization occurs through three different mechanisms to form BO4 tetrahedra with surface oxygen and nonbridging and bridging oxygen. The electronic structure was analyzed to understand the nature of these mechanisms. The conversions from BO3 to BO4 are mostly irreversible as a large number of newly formed BO4 remain unchanged under the decompression. In addition, the formation of a sodium-rich layer can be observed when the systems were compressed to high pressure. Our simulation provides insight into sodium borate glass responses to extreme condition and the underlying electronic mechanisms that can account for these behaviors.

中文翻译：

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承压硼酸钠玻璃中压力诱导的结构转变机理。

本文通过密度泛函理论模拟研究了硼酸钠xNa2O·（100-x）B2O3（x = 25、33、50和60 mol％）在0和10 GPa之间的压缩/减压过程中的结构适应性。硼酸钠被限制在两个Fe2O3衬底之间，并通过减小两个表面之间的间隙进行压缩。结果揭示了硼酸盐通过两阶段转化对负载的响应：低压重排和高压聚合。引发聚合反应所需的压力直接取决于硼酸钠中四配位（[4] B）硼的含量。我们发现聚合反应是通过三种不同的机理发生的，以与表面氧以及非桥连和桥连的氧形成BO4四面体。对电子结构进行了分析，以了解这些机制的性质。从BO3到BO4的转换几乎是不可逆的，因为大量新形成的BO4在减压下保持不变。另外，当将系统压缩至高压时，可以观察到富钠层的形成。我们的仿真提供了对硼酸钠玻璃对极端条件的响应以及可以解释这些行为的潜在电子机制的见解。