| About this Abstract |
| Meeting |
MS&T21: Materials Science & Technology
|
| Symposium
|
Materials vs Minerals: Bridging the Gap between Materials Science and Earth and Planetary Science
|
| Presentation Title |
Coupling Aberration Corrected STEM and DFT to Determine the Crystal Chemistry of Hibonite for Application to Early Solar System Thermodynamics |
| Author(s) |
Pierre-marie Zanetta, Venkat Manga, Yao-Jen chang, Tarunika Ramprasad, Thomas J. Zega |
| On-Site Speaker (Planned) |
Pierre-marie Zanetta |
| Abstract Scope |
Hibonite, CaAl12O19, occurs in refractory inclusions of primitive chondritic meteorites. It is thermodynamically predicted to form at high temperature in the solar nebula gas. Hibonite can host significant amounts of 3d transition metals. In particular, Ti can substitute in multiple oxidation states, reflecting the thermodynamic conditions (temperature, oxygen fugacity; fO2) under which a hibonite grain formed or last equilibrated. Here we describe a study combining electron energy-loss spectroscopy (EELS) in an aberration-corrected scanning transmission electron microscope with first-principles density-functional theory (DFT). The aim is to determine the crystal chemistry as well as the Ti oxidation state and to computationally develop a model to relate Ti4+/ΣTi to the fO2. EELS data show that Ti mostly resides on Al4 sites and that atomic columns contain both Ti4+ and Ti3+. The Ti4+/ΣTi ratio varies over hundreds of nanometers, suggesting that the grain recorded local changes in the redox conditions when it last equilibrated. |