High-pressure Behavior of Framework Minerals

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

Intellectual Merit. Common framework minerals, such as feldspars and perovskites are ubiquitous components of the Earth's crust and lower mantle, respectively, but their structures and properties remain poorly understood because of their complex behavior, especially at high pressure. With the support of two previous NSF-EAR grants, the PIs have gained significant insight into the high-pressure behavior of feldspars and perovskites via development of very precise single-crystal X-ray diffraction techniques to measure small changes in structures at high pressures. This work resulted in a model that successfully predicts phase relations and densities of the pure end member minerals. Funding is requested to extend this work to more natural feldspar and perovskite solid solutions in order to elucidate substitution mechanisms and effects of various element and defect substitutions on elastic and thermodynamic properties. The proposed project will support three new, important initiatives: 1. To determine the crystal chemical principles that control compression of other important groups of framework minerals. 2. To gain an atomic-scale understanding of these principles from electron density calculations. 3. To investigate the dynamics of framework minerals and their role in elasticity. Technical developments will continue to further improve structure determinations at high pressures. The proposed research will contribute towards an ultimate goal to develop a crystal chemical "toolbox" to predict the structural evolution of framework minerals as a function of pressure, temperature and composition. Broader Impacts. This research program will train scientists at all levels, including undergraduates, graduates, postdoctoral scientists and collaborating senior research faculty. Individual studies form the basis of research projects for undergraduates. Graduate students are fully trained in crystallography and mineral physics and are provided opportunities to visit other laboratories and national facilities. Training opportunities are extended to graduate students from other universities through research visits to Virginia Tech. Post-docs are given the opportunity to develop their research skills, and also supervise and train students in the laboratory. The award of this grant will also enable continuation of inter-disciplinary outreach activities, including hosting of a summer crystallography workshop for students and faculty from regional undergraduate institutions. Framework structures attract great interest because of their interesting technological properties. Perovskites, for example, are commonly used as electronic materials, including superconductors, ferroelastics and ferroelectric device materials. Research on the factors that influence the structural state in perovskites has attracted interest outside the earth science community and it is expected that results obtained with this grant will have application in materials sciences and engineering.