岩石中过氧缺陷和空穴的物理解释第一部分：温度的影响
Paradox of Peroxy Defects and Positive Holes in Rocks - Part I: Effect of Temperature
摘要：
过氧缺陷普遍存在于火成岩和高级变质岩矿物中，但过去却被普遍忽视。感兴趣的电荷载流子是正空穴，化学上等价于O $^{2-}$基质中的O $^-$，在O $^{2-}$子晶格中的物理缺陷电子，高度移动，能够快速传播且传播得远。O $^-$相对于O $^{2-}$被氧化。因此，O $^-$不应该存在于来自地壳或上地幔深处的矿物和岩石中，那里的环境非常减少。为了了解过氧缺陷是如何引入的，我们看看过氧缺陷的晶体学和成分特征良好的模型系统：单晶名义上高纯度氧化镁，从熔体中生长在高度还原条件下。在结晶过程中，MgO晶体通过将痕量的H $_2$ O溶解到MgO基质中而引入OH $^-$，导致固溶体（ss）Mg $_{1-δ}$（OH）$_{2δ}$ O $_{1-2δ}$，其中$δ$ <1。在冷却过程中，ss转变成亚稳态的过饱和固溶体（sss）。在进一步冷却过程中，Mg $^{2+}$空位处的OH $^-$对重排其电子，经历氧化还原转化，这导致过氧阴离子O $_2^{2-}$加上分子H $_2$。由于扩散移动，H $_2$可以离开它们的Mg $^{2+}$空位，留下阳离子缺乏的Mg $_{1-δ}$ O。在再加热过程中，O $_2^{2-}$分解，释放出影响电导率行为的空穴载流子。在岩石中，在温度窗口中观察到电导率的类似变化，其中O $_3$ Si-OO-SiO $_3$型过氧缺陷破裂。它们释放出正空穴，控制着地热沿线的电导率响应。
英文摘要：
Though ubiquitous in minerals of igneous and high-grade metamorphic rocks, peroxy defects have been widely overlooked in the past. The charge carriers of interest are positive holes, chemically equivalent to O$^-$ in a matrix of O$^{2-}$, physically defect electrons in the O$^{2-}$ sublattice, highly mobile, able to propagate fast and far. O$^-$ are oxidized relative to O$^{2-}$. As such O$^-$ are not supposed to exist in minerals and rocks that come from deep within the Earth crust or upper mantle, where the environments are overwhelmingly reduced. In order to understand how peroxy defects are introduced, we look at peroxy defects in a crystallographically and compositionally well characterized model system: single crystals of nominally high-purity MgO, grown from the melt under highly reducing conditions. During crystallization the MgO crystals incorporate OH$^-$ through dissolution of traces of H$_2$O into the MgO matrix, leading to a solid solution (ss) Mg$_{1-δ}$(OH)$_{2δ}$O$_{1-2δ}$, where $δ$ <1. During cooling, ss turns into a metastable supersaturated solid solution (sss). During further cooling, OH$^-$ pairs at Mg$^{2+}$ vacancy sites rearrange their electrons, undergoing a redox conversion, which leads to peroxy anions, O$_2^{2-}$, plus molecular H$_2$. Being diffusively mobile, the H$_2$ can leave their Mg$^{2+}$ vacancy sites, leaving behind cation-deficient Mg$_{1-δ}$O. During reheating O$_2^{2-}$ break up, releasing positive hole charge carriers, which affect the electrical conductivity behavior. In rocks, similar changes in the electrical conductivity are observed in the temperature window, where peroxy defects of the type O$_3$Si-OO-SiO$_3$ break up. They release positive holes, which control the electrical conductivity response along the geotherm.
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