<p> </p>
<div style="margin: 0in 0in 0pt">When matters are subjected to extreme compression, unusual phenomena emerged.</div>
<div style="margin: 0in 0in 0pt">For example, new structural types (modulated or incommensurate or</div>
<div style="margin: 0in 0in 0pt">modulated-incommensurate) not exist under ambient conditions are observed.</div>
<div style="margin: 0in 0in 0pt">These phases often exhibit novel electronic properties, For example, it was shown that under high pressure simple elemental (e.g. Li) and molecular solids (e.g. SiH4) became good superconductors [1,2] and "free electron" metals, such as Li and Na, transformed into insulators [3]. It has been suggested that hydrogen may behave like a quantum fluid even at 0K!! These observations and predictions apparently defy explanation from the conventional concepts of chemical bonding. In this presentation, I will introduce a unified view of electronic structure at high pressure and attempt to explain these novel properties [4,5]. New experimental and theoretical methods developed for the elucidation and prediction of crystal structure [6] and electron topology [7] and the relevance of these new techniques to materials design are highlighted.</div>
<div style="margin: 0in 0in 0pt"> </div>
<div style="margin: 0in 0in 0pt">References</div>
<div style="margin: 0in 0in 0pt">[1] J.S. Tse, Y. Yao and K. Tanaka, Novel superconductivity in metallic SnH4 under high pressure, Phys. Rev. Lett., 98, 117004 2007 [2] M. Eremets, I.A. Trojan, S.A. Medvedev, J.S. Tse and Y. Yao, Superconductivity in Hydrogen Dominant Materials: Silane, Science, 319, 1506 2008.</div>
<div style="margin: 0in 0in 0pt">[3] Y. Yao, J.S. Tse, and D.D. Klug, Structures of insulating phases of dense lithium, Phys. Rev. Lett., 102, 115503, 2009.</div>
<div style="margin: 0in 0in 0pt">[4] J.S. Tse, G. Frapper, A. Ker, R. Rousseau, and D. D. Klug. Phase stability and electronic structure of K-Ag intermetallics at high pressure.</div>
<div style="margin: 0in 0in 0pt">Phys.Rev.Lett. 82:4472, 1999.</div>
<div style="margin: 0in 0in 0pt">[5] J.S. Tse, Crystallography of High Pressure Elemental Solids, Z. Krist., 220,</div>
<div style="margin: 0in 0in 0pt">521 2005</div>
<div style="margin: 0in 0in 0pt">[6] J.S. Tse, R. Flacau, S. Desgreniers and J.Z. Jiang, Electron density topology of high-pressure Ba8Si46 from a Rietveld and maximum-entropy analysis, Phys. Rev. B, 76, 174109, 2007.</div>
<div style="margin: 0in 0in 0pt">[7] J.S. Tse, Boron charged under Pressure, Nature, 457, 800, 2009.</div>
<div style="margin: 0in 0in 0pt"> </div>
<p> </p>Dept. of Physics, University of Saskatchewan2009-09-10T18:31:33-07:00Yoo78Fulmer 438Prof. John S. TseThe Physics and Chemistry of "Particle-in-a-box"2009-11-03T15:28:25-08:00