Extended Defects in Olivine and their Impact on Diffusive Reaction Kinetics

本计划包括一项实验研究，以检验(a)热力学势的影响？温度，压力，特别是氧，氧化物和卤化物的化学势？关于橄榄石中扩展缺陷的形成和持续，以及(b)这种扩展缺陷对稀土阳离子和卤化物阴离子输运系数的影响。用于表征缺陷的分析技术强调高分辨率，能量过滤透射电子显微镜（TEM； HRTEM）和（局部电极）原子探针断层扫描（APT； LEAPTM）。提议的APT工作是发展性的：我们是岩石学界最早尝试应用这项有前途的技术的研究人员之一。在哪种情况下可以确定晶体中特定原子（以及可能的同位素）的位置？对矿物（一级是电子绝缘体）和矿物反应的表征。地球和行星科学界要理解类地行星的热力学和热化学演化，就需要对硅酸盐和氧化物矿物及其熔体中的离子扩散动力学有深刻而灵活的理解。由于地质系统中化学成分的数量，有各种各样的动力学路径可用于扩散影响的反应，特别是在高驱动电位的条件下，即，当相互失去平衡的相突然接触时。这种情况在自然界中经常发生；它几乎总是发生在用来理解矿物动力学的实验中。例如，这项研究直接解决了目前岩石学中的一个争议，即在不同的实验中测量了镁铁橄榄石中稀土阳离子的输运系数。都被认为是权威的和好的？？但却显示出几乎104的动力学差异！预计在较快的情况下橄榄石中的亚稳态（也许是瞬态）缺陷结构；我们将描述这些结构，它们的热化学持久性和它们对动力学的影响。该项目将(a)在岩石学、矿物物理学和离子材料科学的这些特定方面教育一名研究生，(b)辨别APT/LEAPTM应用于矿物和合成多组分氧化物的可能性和发展方法。该研究还应用于电池和燃料电池中用作氧化物电极的新材料的设计和表征。我们的工作将着重于岩石学；然而，我们意识到这项研究在能源技术方面满足社会需求的潜力。

This project comprises an experimental study examining (a) the effects of thermodynamic potentials?temperature, pressure and, particularly, chemical potentials of oxygen, oxides and halides?on the formation and persistence of extended defects in olivine and (b) the effect of such extended defects on transport coefficients of rare earth cations and halide anions. The analytical techniques to be employed for characterization of the defects emphasize high-resolution, energy-filtered transmission electron microscopy (TEM; HRTEM) and (local-electrode) atom-probe tomography (APT; LEAPTM). The proposed APT work is developmental: we are among the earliest investigators in the petrology community attempting to apply this promising technique?in which one can characterize the location within a crystal of specific atoms (and potentially isotopes)?to the characterization of minerals (which are, to first order, electronic insulators) and of mineral reactions.The capability of the Earth and planetary sciences community to understand the thermomechanical and thermochemical evolution of the terrestrial planets requires a deep and supple understanding of ionic diffusive dynamics in silicate and oxide mineral and their melts. Because of the number of chemical components in geological systems, there are a variety of kinetic paths available for diffusion-effected reactions, particularly under conditions of a high driving potential, i.e., where phases out of equilibrium with one another are suddenly placed in contact. This situation happens frequently in nature; it happens almost always in experiments used to understand mineral dynamics. For example, this research addresses directly a current controversy in petrology where the transport coefficient for rare-earth cations in ferromagnesian olivine has been measured in different experiments?both considered authoritative and ?good??and yet indicate a kinetics difference of almost 104! Metastable (and perhaps transient) defect structures in olivine in the faster case are anticipated; we will characterize these structures, their thermochemical persistence and their impact on dynamics. This project will (a) educate a graduate student in these particular aspects of petrology, mineral physics and ionic materials science and (b) discern the possibilities and develop the approaches of APT/LEAPTM for application to minerals and synthetic, multicomponent oxides. The research has application, also, to the design and characterization of new materials for use as oxide electrodes in batteries and fuel cells. Our work will emphasize petrology; we are, however, aware of the potential of the research for societal needs with regards to energy technology.