杂质(Na,Al,K,Ca)和相变对石英电导率影响的实验研究及其地学应用启示

Quartz is one of the most important rock-forming minerals, which widely occurs in many kinds of rocks, veins and ores, and it has many kinds of polymorphism as increasing pressure and temperature in the Earth's interior. Result of electrical conductivity of quartz is one of the most important information to study the variety of certain physical and chemical properties in the Earth's interior. In this project, we will first, measure the content of several impurities(Na,Al,K,Ca) by LA-ICP-MS method, and then measure the impedance spectroscopy of quartz and its high pressure polymorphisms at different temperature(500-1900 K) and pressure(1.0-12.0 GPa) conditions in situ; secnd, try to obtain the equivalent circuit diagram of the conduct and activate progress based on the isomorphism model of substitution compensation of Al-Si and the impurities content; third, calculate electrical conductivity by using least square method with the equivalent circuit diagram based on the impedance spectroscopy results, and then calculate the crystal point defect's thermodynamics parameters; finally, study the effects of impurities and phase transition on the electrical conductivity of quartz and its high pressure polymorphisms. We believe this result can be used to research the inter-diffusion progress of quartz with other minerals at high pressure and high temperature, and supply basic parameters for the tomography of the structure and composition in the Earth's interior, and also be used as a basis for scientific usage and properties modification of quartz materials.

石英是地壳中最主要的造岩矿物之一，并广泛存在于多种岩石、脉体和矿石中，且随着温度压力的变化，其在地球内部存在多种同质多像体；其电导率的测定结果对研究地球内部的物理化学性质变化起着至关重要的作用。本项目拟首先利用LA-ICP-MS微区微量元素分析技术获得石英样品的杂质浓度剖面；然后在高温(500-1900 K)高压(1.0-12.0 GPa)条件下原位测量石英及其高压同质多像体的阻抗谱；继而，结合样品杂质浓度剖面合理选择表征样品导电与极化过程的等效电路，获得不同温度和压力下的电导率以及各种杂质缺陷的特征参数；最终，研究高温高压下杂质和相变对石英电导率的影响。该成果为深入研究含石英岩石各矿物间在高温高压下的互扩散过程、利用大地电磁测深数据反演地球内部物质组成与结构、解释地球内部局部区域电导率异常等提供基本参数，同时为石英材料的科学利用与改性研究提供重要的科学依据。

高温高压条件下单晶SiO2的电学性质研究一直受到物理学家和矿物学家们的广泛重视。本工作首先用LA-ICPMS方法测定了石英样品中各种杂质的行亮，之后借助YJ-3000t压力机和Solartron-1260阻抗/增益相位分析仪，在高温高压下系统地测定了不同杂质含量的α-石英 (500~800 ℃、0.5~2.0 GPa)、β-石英 (900~1200℃ ℃、0.5~2.0 GPa) 和柯石英 (773 ~1073 K、4.5~6.5 GPa) 的电导率，取得了如下结果：①在晶丫片 (垂直C轴) 两侧水晶中的各种杂质含量都成很好的对称分布，而自晶丫片沿C轴向向外的单方向，各种杂质的加和含量和相对含量均随距晶丫片距离不同而发生显著变化；②随着温度的上升，α-石英、β-石英和柯石英的电导率均上升，且电导率的对数与1000/T的关系均符合Arrhenius关系，说明三种相态下的导电机制均为离子导电；③β-石英的活化焓和柯石英的活化焓均略低于α-石英，α-石英和柯石英的活化焓和指前因子的变化趋势均是随着压力的上升而上升；④相同温压条件下，α-石英电导率和杂质Li、Na、Al的含量呈正相关关系，α-石英的指前因子 logA和活化焓E的变化趋势均和Li、Na、Al的含量变化趋势一致，且压力很难对Al3+-M+离子对的分解产生明显影响。上述有关单晶SiO2电学性质的实验规律可借助Al3+-Si4+补偿类质同像模型和杂质离子导电与极化模型得到很好的解释。