报告人：Shengbai Zhang，Department of Physics, Applied Physics andAstronomy, Rensselaer Polytechnic Institute

报告时间：2019年5月28日10:00

报告地点：中心校区物理楼333报告厅

摘要：

A crystal is often described as a stackingof a repetitive unit, i.e., the unit cell, with a specific symmetry. While sucha description is tremendously successful in describing the physical propertiesof a crystal, unfortunately, it is often powerless in revealing the relationshipbetween compressed phases of different symmetries. Taking the family of metaldioxides (MO₂) as an example, the structural evolution, subject to afixed chemical formula and highly confined space, often appears as a set ofrandom and uncorrelated events. Here, I will present an alternative way totreat the compressed crystals as a stacking of coordination polyhedrons fromwhich a unified structural transition pattern emerges. Our combined X-raydiffraction (XRD) experiments and first-principles calculations reveal that theincrease of the coordination number happens often only at one of the apexes of thepolyhedron in an orderly fashion, leaving the basal plane and other apexestopologically intact. The chemistry of MO₂evolves accordingly bygiving away its ionicity in exchange for covalency under pressure, in line withthe increased polyhedron sharing.

[1] S.-Y. Xie, et al., J. Phys. Chem. Lett. 2018, 9, 2388-2393.

简介：

Prof. Zhang’sresearch involves first-principles calculations, theory, and modeling ofstructural and electronic properties of condensed matter by using the petaflopcomputational facilities at RPI’s Center for Computational Innovations (CCI).Research directions are largely clean-energy and electronic-applicationsdriven. In particular, he pioneered first-principles theory of defects insemiconductors in the late eighties and since then he has studied numerousdefects, especially those in photovoltaic semiconductors. He pioneeredfirst-principles theory of unconventional coordination chemistry of molecularhydrogen on open metal sites as a possible means to store hydrogen on board. Healso has a longtime exposure to the physics and chemistry of semiconductornanostructures and surfaces. In recent years, He studies water splitting,ultrafast phase change memory, topological insulators, Weyl semimetals,nano-catalysis, two-dimensional materials, chalcogenide perovskites,monolayer-thick high-temperature superconductor films, and real-time carrierdynamics. He has published 350 peer-reviewed papers in journals including 58 PhysicalReview Letters, with over 27,900 total citations (Hirsch Index = 77) by GoogleScholar’s count.

主办单位：尊龙凯时物理学院