Extended Defects in Olivine and their Impact on Diffusive Reaction Kinetics

该项目包括一项实验研究，考察(A)热力学势--温度、压力，特别是氧、氧化物和卤化物的化学势--对橄榄石中扩展缺陷的形成和持久性的影响，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、能量过滤的透射电子显微镜(TEM；HRTEM)和(局部电极)原子探针断层扫描(APT；LEAPTM)。拟议的APT工作是发展的：我们是岩石界最早的研究人员之一，试图将这项有希望的技术应用于矿物(一级电子绝缘体)和矿物反应的表征中，这种技术可以表征特定原子(和潜在的同位素)在晶体中的位置。地球和行星科学界了解类地行星的热机械和热化学演化的能力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入和充分的了解。由于地质系统中化学组分的数量，扩散影响的反应有多种动力学路径可用，特别是在高驱动势条件下，即相互之间失去平衡的相突然接触。这种情况在自然界中经常发生；它几乎总是发生在用来了解矿物动力学的实验中。例如，这项研究直接解决了当前岩石学中的一个争议，即在不同的实验中测量了稀土阳离子在铁镁橄榄石中的迁移系数--都被认为是权威的和良好的？？但却表明动力学差异几乎为104！预计在较快的情况下，橄榄石中的亚稳态(可能是瞬时)缺陷结构；我们将表征这些结构，它们的热化学持久性及其对动力学的影响。该项目将(A)在岩石学、矿物物理和离子材料科学的这些特定方面对研究生进行教育，(B)发现APT/LEAPTM应用于矿物和合成多元氧化物的可能性并开发方法。这项研究还可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。我们的工作将侧重于岩石学；然而，我们意识到能源技术方面的社会需求研究的潜力。

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.