Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B2: Novel Chemistry under Extreme ConditionsFocus
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Sponsoring Units: DCOMP DCP SHOCK Chair: Michael Pravica, University of Nevada Las Vegas Room: 261 |
Monday, March 13, 2017 11:15AM - 11:51AM |
B2.00001: Computational Design of Novel Compounds and Room-temperature Superconductors at High Pressure Conditions Invited Speaker: Yanming Ma Pressure, which is a fundamental thermodynamic control on materials' properties, reduces inter-atomic distances and profoundly modifies electronic orbitals and bonding patterns. High pressure has been a versatile tool for creating exotic materials that are not accessible at ambient conditions. Recently, crystal structure prediction has played a leading role in major high-pressure discoveries. Among various structure prediction methods, CALYPSO method [1] (\underline {http://www.calypso.cn}) is developed on top of swarm-intelligence algorithms by taking the advantage of swarm structures smart learning. Application of CALYPSO into prediction of high-pressure structures has generated a number of exciting discoveries. Examples point to the predicted chemical reactions of Fe/Ni-Xe and Au-Li at high pressures with the formation of unusual compounds Fe$_{\mathrm{3}}$/Ni$_{\mathrm{3}}$Xe and AuLi$_{\mathrm{4}}$/Li$_{\mathrm{5}}$, respectively [2-3]. Motivated by our theory, the Fe$_{\mathrm{3}}$/Ni$_{\mathrm{3}}$Xe compounds were recently experimentally synthesized, providing a possible solution on ``missing Xe paradox'' towards to Xe storage inside Earth core. Here, Au loses its chemical identity, and acts as a 6p element by achieving high negative oxidation state ($\ge $-2). Our prediction of high-T$_{\mathrm{c}}$ superconductivity on highly compressed H$_{\mathrm{2}}$S [4] initiated the recent experimental observation of record high 200 K superconductivity in H$_{\mathrm{3}}$S. Perspective towards to the design of room-T superconductors in compressed H-rich materials will be presented, including design of high $T_{\mathrm{c\thinspace }}$(\textgreater 100 K) superconductor of TeH$_{\mathrm{4}}$, the highest H-content superconductor in chalcogen hydrides [5]. References: [1] Y. Wang, J. Lv, L.Zhu, and Y. Ma, Phys. Rev. B 82, 094116 (2010); Comput. Phys. Commun. 183, 2063 (2012). [2] L. Zhu, et al, Nature Chem. 6, 644 (2014). [3]G. Yang, \textit{et al.}, J. Am. Chem. Soc. 138, 4046 (2016). [4] Y. Li, et al, J. Chem. Phys. 140, 174712 (2014). [5] X. Zhong, \textit{et al,} Phys. Rev. Lett. 116, 057002 (2016). [Preview Abstract] |
Monday, March 13, 2017 11:51AM - 12:03PM |
B2.00002: Reactivity of Noble Gases under High Pressure Jorge Botana, Xiaoli Wang, Jakoah Brgoch, Frank Spera, Mathew Jackson, Georg Kresse, Haiqing Lin, Maosheng Miao There has been recently a trend in finding how high pressure can enable the reactivity of noble gases (NG). The discovery of Xe oxidation meant a doctrinal change, by showing that a complete electron shell is not inert to reaction. However reduced NG atoms in chemical compounds were not found, neither experimentally nor theoretically. Using first-principles electronic structure calculations coupled with a structure prediction method, we have found that Xe, Kr, and Ar can form thermodynamically stable compounds with Mg at high pressure ($\geq 125$, $\geq 250$, and $\geq 250$ GPa, respectively). The compounds are metallic and the NG atoms are negatively charged, suggesting that chemical species with a completely filled shell become reduced. Moreover, Mg$_2$NG are high-pressure electrides. Inspired by recent research,\footnote{\tt arXiv:1309.3827 [cond-mat.mtrl-sci]} we extended the study to the mixtures of different compounds of Mg, Li and N with He. We performed a systematic structure search from $10^{-4}$ to $300$ GPa for mixtures with different ratios of He. [Preview Abstract] |
Monday, March 13, 2017 12:03PM - 12:15PM |
B2.00003: Metallic surface states in elemental high-pressure electrides Ivan Naumov, Russell Hemley In their high-pressure insulating electride phases, the alkali metals Li, Na, and K are unique insulating materials that can be considered as both ionic and covalent. Using a Berry phase analysis we show that such dual chemical character leads to two types of metallic surface states depending on surface termination/orientation. As covalent materials with an inverted $s-p$ bulk band gap, these high-pressure electrides tend to form metallic Shockley-type surface states within the gap. On the other hand, as ionic materials, they have polar surfaces that exhibit metallic surface states due to ``electronic reconstruction'' in which the electrons move from the valence band on one surface to the conduction band at the opposite surface, thereby making both the surfaces metallic. The results provide predictions for future measurements. This research was supported by EFree, an Energy Frontier Research Center funded by the U.S. DOE, Office of Science, Basic Energy Sciences (award DE-SC0001057). The infrastructure and facilities used were supported by the U.S. DOE/NNSA (award DE-NA-0002006, CDAC). Work at LLNL was performed under the auspices of the DOE (contract DE-AC52-07NA27344). [Preview Abstract] |
Monday, March 13, 2017 12:15PM - 12:27PM |
B2.00004: Quasimolecules in compressed Lithum Maosheng Miao, Roald Hoffmann, Jorge Botana, Ivan Naumov, Rossell Hemley Electrides are materials in which some valence electrons are separated from all atoms and occupy interstitial regions, effectively forming anions with no centering nuclei nor core electrons. Recently, it is found that, under high pressure, alkali metals such as Li and Na become semiconducting or insulating. As they do so, they adopt structures containing sites that accommodate electrons, leading to the formation of high-pressure electrides (HPE). Similar phenomena have also been predicted for Mg, Al and several other materials. The driving force for HPE formation may be attributed to the lack of core electrons in the interstitial sites, which causes the energies of the corresponding quantized orbitals to increase less significantly with pressure than normal atomic orbitals. These empty sites enclosed by surrounding atoms have been termed interstitial quasiatoms (ISQ); they may show some of the chemical features of atoms, including the potential of forming covalent bonds. Here we argue that some calculated ISQs in the high-pressure semiconducting Li phase (oC40, \textit{Aba}2) actually form covalently bonded pairs. We suggest such quasimolecules may be found in other systems at high pressures as well. [Preview Abstract] |
Monday, March 13, 2017 12:27PM - 12:39PM |
B2.00005: Search for high-Tc conventional superconductivity at megabar pressures in the lithium-sulfur system Lilia Boeri, Christian Kokail, Christoph Heil Motivated by the recent report of superconductivity above 200 K in ultra-dense hydrogen sulfide, we search for high-T$_c$ conventional superconductivity in the phase diagram of the binary Li-S system, using ab initio methods for crystal structure prediction and linear response calculations for the electron-phonon coupling. We find that at pressures higher than 20 GPa, several new compositions, besides the known Li$_2$S, are stabilized; many exhibit electride-like interstitial charge localization observed in other alkali-metal compounds. Of all predicted phases, only an fcc phase of Li$_3$S, metastable before 640 GPa, exhibits a sizable T$_c$, in contrast to what is observed in sulfur and phosphorus hydrides, where several stoichiometries lead to high T$_c$. We attribute this difference to 2$s$-2$p$ hybridization and avoided core overlap, and predict similar behavior for other alkali-metal compounds. [1] C. Kokail, C. Heil and L. Boeri, Phys. Rev. B 94, 060502 (R) (2016) [Preview Abstract] |
Monday, March 13, 2017 12:39PM - 12:51PM |
B2.00006: Pressure-induced Transformations of Dense Carbonyl Sulfide to Singly Bonded Amorphous Metallic Solid Minseob Kim, Ranga Dias, Yasuo Ohishi, Takahiro Matsuoka, Jing-Yin Chen, Choong-Shik Yoo The application of internal or external pressure transforms molecular solids into non-molecular extended solids with diverse crystal structures and electronic transport properties. Here, we present pressure-induced phase transitions and associated structural and electric transitions of carbonyl sulfide (OCS) using Raman spectroscopy, X-ray diffraction, resistivity measurement and pair distribution function (PDF) analysis. Linear molcular OCS(R3m, Phase I) transforms to bent OCS (Cm, Phase II) at 9 GPa, an amorphous, one-dimensional (1D) polymer at 20 GPa (Phase III), and an extended 3D network above ~35 GPa (Phase IV) that metallizes at ~105 GPa. Series of phase transformations reveal that long-range dipole interaction plays an important role in the transition regime of dense molecular solid and intermediate nature of OCS between its two isovalent end members of CO$_2$ and CS$_2$ leads to an important chemical concept for the extended molecular alloy. [Preview Abstract] |
Monday, March 13, 2017 12:51PM - 1:27PM |
B2.00007: Barochemistry: Predictive Solid State Chemistry Invited Speaker: Choong-Shik Yoo The application of compression energy comparable to that of chemical bonds, but substantially greater than those of defects and grain boundaries in solids allows us to pursue novel concepts of high-pressure chemistry (or barochemistry) in materials development by design. At such extreme pressures, simple molecular solids covert into densely packed extended network structures that can be predicted from first principles. In recent years, a significant number of new materials and novel extended structures have been designed and discovered in highly compressed states of the first- and second- row elemental solids, including Li, C, H$_{2}$,$_{\, }$N$_{2}$, O$_{2}$, CO, CO$_{2}$, and H$_{2}$O. These extended solids are extremely hard, have high energy density, and exhibit novel electronic and nonlinear optical properties that are superior to other known materials at ambient conditions. However, these materials are often formed at formidable pressures and are highly metastable at ambient conditions; only a few systems have been recovered, limiting the materials within a realm of fundamental scientific discoveries. Therefore, an exciting new research area has emerged on the barochemistry to understand and, ultimately, control the stability, bonding, structure, and properties of low Z extended solids. In this paper, we will present our recent research to develop hybrid low Z extended solids amenable to scale up synthesis and ambient stabilization, utilizing kinetically controlled processes in dense solid mixtures and discuss the governing fundamental principles of barochemistry. [Preview Abstract] |
Monday, March 13, 2017 1:27PM - 1:39PM |
B2.00008: Benzene-derived nanothreads Maria Baldini, Xiang Li, Bo Chen, En-shi Xu, Tao Wang, Vincent H. Crespi, Sabri Elatresh, Roald Hoffman, James J. Moliason, Christopher A. Tulk, Malcolm Guthrie, John V. Badding The benzene pressure -- temperature phase diagram has been widely studied. An irreversible phase transformation to an amorphous hydrogenated carbon occurs after compressing benzene to 20 GPa [1-6]. Later synthesis of a crystalline one-dimensional sp3 carbon nanomaterial by a kinetically controlled high-pressure solid-state reaction of benzene was reported [7,8]. These benzene-derived nanothreads may be the first member of a new class of ordered sp3 nanomaterials with unique promise for a diverse range of energy applications [7,8]. We report in-situ Raman and X-ray diffraction characterization of the formation of nanothreads at high pressure. Nanothread formation begins at 14 to 20 GPa, as documented by the appearance of a new diffraction signature. The crystal-to-crystal transformation from solid benzene to nanothreads will be discussed. [Preview Abstract] |
Monday, March 13, 2017 1:39PM - 1:51PM |
B2.00009: Dense Carbon Monoxide to 160 GPa: Stepwise Polymerization to Two-Dimensional Layered Solid. Young Jay Ryu, Minsoeb Kim, Ranga Dias, Dennis Klug, Choong-Shik Yoo Carbon monoxide (CO) is one of simple molecular systems like N$_{\mathrm{2}}$, O$_{\mathrm{2}}$ and H$_{\mathrm{2}}$, yet been studied at pressures above 5-10 GPa. It is also the first molecular system found to transform into a nonmolecular “polymeric” solid in high energy density at 5.5 GPa; yet, little is known about its structure and transformation beyond this pressure. This imposes a serious short fall in understanding high-pressure behaviors of heteronuclear diatomic systems like CO in comparison with those of homonuclear diatomic systems like N$_{\mathrm{2}}$. Here, we present a series of pressure-induced phase transformations in CO to 160 GPa: from a molecular solid to a highly colored, low-density polymeric phase I to translucent, high-density phase II to transparent, and indirect-gap semi-metallic phase III. The properties of these polymorphs are consistent with those expected from recently predicted \textit{1D} \textit{P2}$_{1}/m,$ \textit{3D} \textit{P2}$_{1}$\textit{2}$_{1}$\textit{2}$_{1}$, and \textit{2D} \textit{Cmcm} structures, respectively. Thus, the present results suggest a stepwise polymerization of CO triple bonds to ultimately a \textit{2D} singly bonded layer structure, as recently found in dense nitrogen (LP-N) [Preview Abstract] |
Monday, March 13, 2017 1:51PM - 2:03PM |
B2.00010: Synthesis of Hf$_8$O$_7$, a new binary hafnium oxide, at high pressures and high temperatures Bjorn Winkler, Lkhamsuren Bayarjargal, Wolfgang Morgenroth, Nadine Schrodt, Victor Milman, Christopher Stanek, Blas Uberuaga Two binary phases in the system Hf-O have been synthesized at pressures between 12 and 34 GPa and at temperatures up to 3000\,K by reacting Hf with HfO$_2$ using a laser-heated diamond anvil cell. In situ X-ray diffraction in conjunction with density functional theory calculations have been employed to characterize a previously unreported tetragonal Hf$_8$O$_7$ phase. This phase has a structure which is based on a fcc Hf packing with oxygen atoms occupying octahedral interstitial positions. Its predicted bulk modulus is 223(1) GPa. The second phase has a composition close to Hf$_6$O, where oxygen atoms occupy octahedral interstitial sites in a hcp Hf packing. Its experimentally determined bulk modulus is 128(30) GPa. The phase diagram of Hf metal was further constrained at high pressures and temperatures, where we show that $\alpha$-Hf transforms to $\beta$-Hf around 2160(150) K and 18.2 GPa and $\beta$-Hf remains stable up to at least 2800 K at this pressure. [Preview Abstract] |
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