Emergent Materials under Extremes and Decisive In-situ Characterizations: Pressure-induced Dramatic Changes in Structures and Properties I
Program Organizers: Xujie Lu, Center for High Pressure Science & Technology Advanced Research; Judith Driscoll, University of Cambridge; Xiaofeng Guo, Washington State University; Hua Zhou, Argonne National Laboratory

Wednesday 8:30 AM
October 2, 2019
Room: E145
Location: Oregon Convention Center

Session Chair: BingBing Liu, Jilin University; Xujie Lu, Center for High Pressure Science & Technology Advanced Research

8:30 AM  Invited
Emerging Materials from Pressure Induced Electronic Transition: Wenge Yang1; 1HPSTAR
    Pressure as a clean tuning tool, has been extensively used to explore novel properties of materials that cannot be realized at ambient conditions. Under pressure, the electronic configuration involving valence and inner shell electrons can be largely re-arranged to minimize the total energy, which leads to charge transfer, spin crossover, and even forming new bonds. As a result, emerging phenomena such as carrier-type switching, carrier density increasing, excitation state lifetime change, insulator-to-metal and even superconducting transition, and giant enhancement in piezoelectricity have been observed. In this talk, we like to present the recent high pressure studies on the abnormal transport properties of topologic Dirac semimetals, enhancement in electronic transport and photoelectric properties in bismuth oxysulfide, and extending the lifetime of photoluminescence in hydride perovskite. With a suite of characterization tools, we explored their electronic transition mechanism which provides guideline to develop the novel route to realize them at ambient conditions.

9:00 AM  Cancelled
High-pressure Chemistry: Novel Compounds and Bond Schemes: Alexander Goncharov1; 1Geophysical Laboratory, Carnegie
    A major focus of the field of Chemistry is the prediction as to how various atoms form bonds, and how such bonding controls the structure and properties of matter. The majority of matter in the Universe resides at extreme pressures and temperatures (P-T) that force atoms into extremely close contact, where very exotic compounds can become stable. Theoretical first principles calculations and laboratory experiments at extreme P-T conditions address this problem. I will present experiments at extreme pressures up to 200 GPa that include recent discoveries of unusual “salts” (KCl3 and XeFe3), stable compounds with noble gasses (Na2He), polyhydrides of Na, U, and S, and N-H polymers among others. These exotic materials hold a promise of potentially unparalleled physical and chemical properties such as high-temperature superconductivity, incompressibility, energy storage capacity, and others. Many of these newly discovered extreme materials are likely to be present in the interiors of the planets.

9:30 AM  
Superconductivity in Amorphous Sb2Se3: Kai Zhang1; Wenge Yang2; 1The University of Chicago; 2HPSTAR
    Here we report reversible pressure induced structure transition sequences of amorphous Sb2Se3, which has attracted considerable attention due to its unusual physical properties. It transformed from low density amorphous (LDA) to high density amorphous (HDA) around 20 GPa, then enters into substitutional body-centered cubic (BCC) phase around 50 GPa. Superconductivity was found in HDA and BCC phases. Superconducting critical temperature Tc continuously increased to 6.32K with applied pressure in HDA and then showed distinct enhancement when transforming into BCC phase, 7.5K.

9:50 AM  Invited
Novel Superhard sp3 Carbon Allotrope from Cold-Compressed C70 Peapods: Liu Bingbing1; 1Jilin University
    Design and synthesis of new carbon allotropes have always been important topics. Here we report a new carbon allotrope, formed from cold-compressed C70 peapods, which most likely can be identified with a fully sp3-bonded monoclinic structure, here named V carbon, predicted from our simulation. Theoretical calculations reveal that V carbon has a Vickers hardness of 90 GPa and a bulk modulus ∼400 GPa, which well explains the “ring crack” left on the diamond anvils by the transformed phase in our experiments. The V carbon is thermodynamically stable over a wide pressure range up to 100 GPa, suggesting that once V carbon forms, it is stable and can be recovered to ambient conditions. A transition pathway from peapod to V carbon has also been suggested. These findings suggest a new strategy for creating new sp3-hybridized carbon structures by using fullerene@nanotubes carbon precursor containing odd-numbered rings in the structures.

10:20 AM Break

10:40 AM  Invited
Structural Behavior and Phase Relations of β-Eucryptite at High P-T Conditions: Hongwu Xu1; 1Los Alamos National Laboratory
    β-eucryptite (LiAlSiO4) has attracted much attention because of its unusual physical properties including near-zero thermal expansion and one-dimensional superionic conductivity. Structurally, β-eucryptite is a derivative of β-quartz (SiO2) in which half the Si4+ cations are replaced by Al3+ and the charge is compensated by the incorporation of Li+ into the structural channels parallel to the c-axis. The unusual thermal expansion of β-eucryptite arises from its parent β-quartz structure, while its superionic conductivity is due to the diffusion of Li+ ions along the structural channels. In this presentation, I will review our systematic studies on the crystal structures and phase stability of β-eucryptite at high pressure (P) and/or high temperature (T) conditions using in situ neutron and synchrotron X-ray diffraction. Thermal expansion coefficients and bulk moduli of β-eucryptite and its stability relations with other associated phases (crystalline and amorphous) have been derived, thereby gauging the P-T range for its technological applications.

11:10 AM Panel Discussion