Prof. Przemyslaw Dera [University of Hawaii at Manoa, USA]

Title: Hypervalent penta-coordinated silicon and meta stable phase transitions in chain silicates

Time: 10:00 - 11:00 AM, Thursday, January 25, 2018

Place: Conference room C206, HPSTAR (Beijing)

Host: Haozhe Liu

Abstract:

Earth is a rocky planet, dominated by silicateminerals, which undergo chemical and physical transformations as a function ofdepth, and thus control properties and dynamics of the planet interior. Globalgeologic phenomena and processes including deep-focus earthquakes and platetectonics are often affected by these transformations. Silicon strongly prefersfour-coordinated crystallographic sites due to the sp3 electronhybridization. As a consequence, in silicate minerals characteristic of shallowEarth interior, including the crust and the upper mantle, silicon residespredominantly in tetrahedral sites coordinated by four oxygen atoms (IVSi).However, silicon is also capable of forming 5- and 6- coordinated states (VSiand VISi). These hypervalent states are favored at higher pressureand with increased ligand electronegativity. There has been great interest inunderstanding the occurrence and properties of the least common,penta-coordinated Si phases (VSi) both in geophysics, as well as insolid state chemistry.  Amorphous solids,melts and liquids can sustain exotic coordination environments such as SiO5more easily due to the lack of symmetry and long-range order. At ambientconditions, crystalline silicate minerals with VSi are extremely rare.In a quest to find previously unknown high-pressure silicate polymorphscharacterized by hypervalent VSi and understand the geophysicalconsequences of their existence, we used a combination of high-pressure synchrotronX-ray diffraction and density functional theory calculations to systematicallyexplore the family of chain silicate minerals, including pyroxenes, pyroxenoidsand amphiboles. This presentation will review systematic phase transitiontrends and new structural varieties that have been discovered. We investigatedthe structural aspects of the new transformations and their effects on latticepreferred orientation and transformation fabrics of the high-pressuremetamorphic rocks. The results suggest that the presence of VSi hasconsequences for chemical reactivity, elastic anisotropy, elastic and plasticdeformation, density of the subducted slab and affects buoyancy relative to thesurrounding mantle.

Biography of the Speaker:





Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa

2016/7-  R5 Researcher (Full Professor, tenured)

2013/8-2016/6 R4 Associate Researcher (Associate Professor, tenure track)

Consortium for Advanced Radiation Sources, University of Chicago

2013/8-2014/8 Visiting Scholar

2010/4-2013/8 Senior Research Associate (tenured)

2007/6-2010/4 Research Beamline Scientist (tenure track)

Geophysical Laboratory, Carnegie Institution of Washington

2003-2007 Associate Staff Scientist (principal investigator)

2002-2003 Senior Research Scientist

2000-2002 Distinguished Barbara McClintock Postdoctoral Fellow

AWARDS AND HONORS

2014-2015  Consortium for Materials Properties Research in Earth Sciences Distinguished Lecturer

2013    Elected Fellow of the Mineralogical Society of America