Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session F20: Materials in Extremes: High-pressure Synthesis of New MaterialsFocus
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Sponsoring Units: DCOMP GSCCM DMP Chair: Jennifer Ciezak-Jenkins, Army Research Laboratory Room: 319 |
Tuesday, March 15, 2016 11:15AM - 11:51AM |
F20.00001: Extreme thermodynamic conditions: novel stoichiometries, violations of textbook chemistry, and intriguing possibilities for the synthesis of new materials. Invited Speaker: Elissaios Stavrou As evidenced by numerous experimental and theoretical studies, application of high pressure can dramatically modify the atomic arrangement and electronic structures of both elements and compounds. However, the great majority of research has been focused on the effect of pressure on compounds with constant stoichiometries (typically those stable under ambient conditions). Recent theoretical predictions, using advanced search algorithms, suggest that composition is another important variable in the search for stable compounds, i.e. that the more stable stoichiometry at elevated pressures is not \textit{a priory} the same as that at ambient pressure. Indeed, thermodynamically stable compounds with novel compositions were theoretically predicted and experimentally verified even in relatively simple chemical systems including: Na-Cl, C-N, Li-H, Na-H, Cs-N, H-N, Na-He, Xe-Fe. These materials are stable due to the formation of novel chemical bonds that are absent, or even forbidden, at ambient conditions. Tuning the composition of the system thus represents another important, but poorly explored approach to the synthesis of novel materials. By varying the stoichiometry one can design novel materials with enhanced properties (e.g. high energy density, hardness, superconductivity etc.), that are metastable at ambient conditions and synthesized at thermodynamic conditions less extreme than that those required for known stoichiometries. Moreover, current outstanding questions, ``anomalies'' and ``paradoxes'' in geo- and planetary science (e.g. the Xenon paradox) could be addressed based on the stability of surprising, stoichiometries that challenge our traditional ``textbook'' picture. In this talk, I will briefly present recent results and highlight the need of close synergy between experimental and theoretical efforts to understand the challenging and complex field of variable stoichiometry under pressure. Finally, possible new routes for the synthesis of novel materials will be discussed. [Preview Abstract] |
Tuesday, March 15, 2016 11:51AM - 12:03PM |
F20.00002: Hydrogen sulfide at high pressure: change in stoichiometry Alexander Goncharov, Sergey Lobanov, Ivan Kruglov, Xiao-Miao Zhao, Xiao-Jia Chen, Artem Oganov, Zuzana Konopkova, Vitali Prakapenka Hydrogen sulfide (H$_{\mathrm{2}}$S) was studied by x-ray synchrotron diffraction (XRD) and Raman spectroscopy up to 144 GPa at 180-295 K. We find that H$_{\mathrm{2}}$S compound become unstable with respect to formation of new compounds with different composition including pure S, H$_{\mathrm{3}}$S and HS$_{\mathrm{2}}$ depending on the thermodynamic P-T path. These results are supported by our quantum-mechanical variable-composition evolutionary simulations that show the stability of the above mentioned compounds at elevated pressures. The stability of H$_{\mathrm{3}}$S at high pressures, which we find a strong experimental and theoretical confirmation here, suggests that it is this material which is responsible for high-temperature superconducting properties reported previously. [Preview Abstract] |
Tuesday, March 15, 2016 12:03PM - 12:15PM |
F20.00003: ABSTRACT WITHDRAWN |
Tuesday, March 15, 2016 12:15PM - 12:27PM |
F20.00004: A possible analog to MgB$_{\mathrm{2}}$: Discovery of a predicted layered LiB via cold compression Aleksey Kolmogorov, Samad Hajinazar, Chris Angyal, Vladimir Kuznetzov, Andrew Jephcoat Stoichiometric LiB has been previously predicted [1,2] to be a new synthesizable layered material with electronic and vibrational properties desired for MgB$_{\mathrm{2}}$-type superconductivity. However, previous experiments showed no signs of the proposed compound forming under high pressures. We report on the synthesis of the LiB via cold compression in the diamond anvil cell [3]. Remarkably, the signature powder XRD peak from the new layered compound appeared above 21 GPa and remained visible down to ambient pressure upon sample quenching. Apparent stacking disorder in LiB and a stoichiometry shift in the starting LiB$_{y}$ (from $y\approx $0.90 down to $y\approx $0.75) made material characterization a challenge. \textit{Ab initio} modeling allowed us to establish the pressure-dependent composition of LiB$_{y}$ and predict related stable structures overlooked in previous studies. [1] A.N. Kolmogorov and S. Curtarolo, Phys. Rev. B 74, 224507 (2006) [2] A.N. Kolmogorov and S. Curtarolo, Phys. Rev. B 73, 180501(R) (2006) [3] A.N. Kolmogorov, S. Hajinazar, C. Angyal, V.L. Kuznetsov, and A.P. Jephcoat, Phys. Rev. B 92, 144110 (2015) [Preview Abstract] |
Tuesday, March 15, 2016 12:27PM - 1:03PM |
F20.00005: Discovering new materials and new phenomena with evolutionary algorithms Invited Speaker: Artem Oganov Thanks to powerful evolutionary algorithms, in particular the USPEX method, it is now possible to predict both the stable compounds and their crystal structures at arbitrary conditions, given just the set of chemical elements. Recent developments include major increases of efficiency and extensions to low-dimensional systems and molecular crystals (which allowed large structures to be handled easily, e.g. Mg(BH$_{\mathrm{4}})_{\mathrm{2}}$ and H$_{\mathrm{2}}$O-H$_{\mathrm{2}})$ and new techniques called evolutionary metadynamics and Mendelevian search. Some of the results that I will discuss include: 1. Theoretical and experimental evidence for a new partially ionic phase of boron, $\gamma $-B and an insulating and optically transparent form of sodium. 2. Predicted stability of ``impossible'' chemical compounds that become stable under pressure -- e.g. Na$_{\mathrm{3}}$Cl, Na$_{\mathrm{2}}$Cl, Na$_{\mathrm{3}}$Cl$_{\mathrm{2}}$, NaCl$_{\mathrm{3}}$, NaCl$_{\mathrm{7}}$, Mg$_{\mathrm{3}}$O$_{\mathrm{2}}$ and MgO$_{\mathrm{2}}$. 3. Novel surface phases (e.g. boron surface reconstructions). 4. Novel dielectric polymers, and novel permanent magnets confirmed by experiment and ready for applications. 5. Prediction of new ultrahard materials and computational proof that diamond is the hardest possible material. [Preview Abstract] |
Tuesday, March 15, 2016 1:03PM - 1:15PM |
F20.00006: Structural study of superconducting sulfur hydride under high pressure Katsuya Shimizu, Mari Einaga, Masafumi Sakata, Harushige Nakao, Mikhail Eremets, Alexander Drozdov, Ivan Troyan, Naohisa Hirao, Yasuo Ohishi Superconductivity exceeding 200 K was recently reported in the highly compressed hydrogen sulfide [1]. The superconductor was found to be synthesized by pressure above 90 GPa under low temperature exceeding 200 K. Here we report our high-pressure structural studies for H$_{2}$S and D$_{2}$S using a synchrotron x-ray at room temperature and low temperature [2]. The sample at 10 GPa was firstly cooled down to 200 K and compressed up to 150 GPa, then cooled down to 10 K. The resistivity and diffraction patterns were monitored at all procedures. The critical temperature and zero resistivity were confirmed. The x-ray diffraction data in both cells showed good agreement with the theoretically predicted structures [3]. [Preview Abstract] |
Tuesday, March 15, 2016 1:15PM - 1:27PM |
F20.00007: High --Pressure Synthesis and Characterization of Incompressible Titanium Pernitride Venkata Bhadram, Duck Young Kim, Timothy Strobel We report the discovery of a new transition-metal pernitride, TiN$_{\mathrm{2}}$, which was synthesized by reacting TiN with N$_{\mathrm{2}}$ at 73GPa in a laser-heated diamond anvil cell (DAC). Our \textit{in situ} pressure dependent x-ray diffraction studies suggest that TiN$_{\mathrm{2\thinspace }}$is recoverable at ambient conditions in a crystal structure that contains single bonded nitrogen units (N$_{\mathrm{2\thinspace }}$dumbbells) embedded in the metal lattice and exhibits high bulk modulus (in the range 360-385 GPa) which is usually observed in superhard materials. We have performed \textit{ab initio} calculations to understand the electronic properties and bonding nature in TiN$_{\mathrm{2}}$ and thereby elucidate the origin of incompressible behavior of this material which is rooted in the nearly filled anti-bonding states of the pernitride units. Although, study of transition metal pernitrides has been an active area of research for quite some time, most of the pernitrides synthesized so far are belong to noble metal group. To our knowledge, this is the first experimental report on TiN$_{\mathrm{2\thinspace }}$which is the only light metal pernitride exhibiting bonding-mechanical property relation that is usually seen in heavy metal pernitrides. [Preview Abstract] |
Tuesday, March 15, 2016 1:27PM - 1:39PM |
F20.00008: Electride-like phases at extreme compression and elevated temperatures Stanimir Bonev, Jonathan DuBois The transformation of materials into electride-like structures under the application of extreme pressure has attracted a lot of interest recently. Theoretical studies have predicted the existence of low-coordinated crystal phases, where the conduction electrons are localized in the interstitial atomic regions, for a number of elements at high density. Most of these works have been limited to static lattice calculations. The pressures where such transformations are projected to occur are accessible in shock-wave experiments, but at elevated temperatures. In this talk I will discuss the temperature dependence of elecride structures, both solids and liquids, as well as the requirements for their accurate simulation. [Preview Abstract] |
Tuesday, March 15, 2016 1:39PM - 1:51PM |
F20.00009: The effects of hydrogenation and high pressure on $\alpha$-tetragonal boron: a first principles study Naoki Uemura, Koun Shirai It is well known that boron rich crystals are superhard materials. $\alpha$-tetragonal ($\alpha$-tet) boron is one of the metastable phase in elemental boron crystals under high temperature and high pressure. This phase has a possibility of including some hydrogen atoms due to the experimental process, but it has not yet been shown crystal structures and electronic properties of hydrogenated $\alpha$-tet boron. Using first-principles calculations, we theoretically predicted stable structures and investigated the influences from hydrogenation of $\alpha$-tet boron and high pressures. According to our calculations, non-bonding states of pure $\alpha$-tet boron, which were mostly occupied by P$_{z}$ like orbitals coming from interstitial boron atoms in $\alpha$-tet boron, were completely vanished by doping some hydrogen atoms and the higher the pressure was, the lager energy gaps between the valence band maximum and the conduction band minimum on $\alpha$-tet boron were. These results provide that the deformation potential depended on the pressure is positive, which is basically negative on semiconductors except for diamonds and is an index of the hardness under pressure on semiconductors. [Preview Abstract] |
(Author Not Attending)
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F20.00010: Creation and formation mechanism of new carbon phases constructed by amorphous carbon. Mingguang Yao, Wen Cui, Bingbing Liu Our recent effort is focusing on the creation of new hard/superhard carbon phases constructed by disordered carbons or amorphous carbon clusters under high pressure. We showed that the pressure-induced amorphous hard carbon clusters from collapsed fullerenes can be used as building blocks (BBs) for constructing novel carbon structures. This new strategy has been verified by compressing a series of intercalated fullerides, pre-designed by selecting various dopants with special features. We demonstrate that the boundaries of the amorphous BBs are mediated by intercalated dopants and several new superhard materials have been prepared. We also found that the dopant-mediated BBs can be arranged in either ordered or disordered structures, both of which can be hard enough to indent the diamond anvils. The hardening mechanisms of the new phases have also been discussed. For the glassy carbon (GC) constructructed by disordered fullerene-like nanosized fragments, we also found that these disordered fragments can bond and the compressed GC transformed into a transparent superhard phase. Such pressure-induced transformation has been discovered to be driven by a novel mechanism (unpublished). By understanding the mechanisms we can clarify the controversial results on glassy carbon reported recently. [Preview Abstract] |
Tuesday, March 15, 2016 2:03PM - 2:15PM |
F20.00011: First-principles study of MoHn (n$=$1, 2 and 3) crystal structures under high pressure Xiaolei Feng, Jurong Zhang, Hanyu Liu, Hui Wang Hydrogen-rich materials have attracted attention recently, owing to their fascinating chemical bonding and potential high superconducting critical temperatures temperature. Inspired by the recent identification of polyhydrides of d metals and molybdenum hydride molecules with a high H content, we explored the crystal structures of MoHn (n~$=$~1, 2, and 3) under high pressures using particle swarm optimization combined with first-principles electronic structure calculations. Several novel structures of MoH2 and MoH3 are predicted at high pressures. MoH is calculated to be stable at ambient pressure; at P~\textgreater ~2.3~GPa the hexagonal phase of MoH2 becomes stable, and at 24~GPa it transforms into an orthorhombic structure, which remains stable up to 100~GPa. All three stable structures show metallic behavior under pressure. The calculated electronic properties suggest that the d-orbitals of the Mo atoms provide the dominant contribution to the density of states at the Fermi level, which is different from the density of states previously predicted for H-rich materials. The present results offer insights in understanding of chemical and physical properties in hydrogen-rich materials, especially in extreme environments. [Preview Abstract] |
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