Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session L31: Focus Session: Materials at High Pressure III: Electronic Transitions |
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Sponsoring Units: DMP GSCCM DCOMP Chair: Koichiro Umemoto, University of Minnesota Room: C145 |
Tuesday, March 22, 2011 2:30PM - 2:42PM |
L31.00001: Pressure Induced Metal Insulator Phase Transition in Eu$_2$Ir$_2$O$_7$ Fazel Fallah Tafti, Jun Ishikawa, Yo Machida, Alix McCollam, Satoru Nakatsuji, Stephen Julian The metal to insulator phase transition of the pyrochlore iridate Eu$_2$Ir$_2$O$_7$ has been studied by means of resistivity measurements under pressure in the range 2 to 12 GPa. At ambient pressure, the system is a ``metal'' at high temperatures with a non-metallic rise of resistivity with decreasing temperature followed by a metal-insulator phase transition at T$_{MI}$ below which it becomes insulating. With increasing pressure, a cross-over from non-metallic to metallic appears in the resistivity curves at a temperature $T^*>T_{MI}$. As the pressure is further increased T$^*$ rises, T$_{MI}$ drops and the low temperature insulating phase melts into a metallic phase through a continuous transition at P $\sim$ 7.8 GPa. The high pressure metallic phase is rather curious and exhibits two characteristic features of Kondo metals: a minimum resistivity and a logarithmic rise of resistivity at low temperatures. We will show that there is a remarkable correspondence between the resistivity curves measured at various pressures and those obtained by successively replacing the R site of the R$_2$Ir$_2$O$_7$ family by larger rare earth atoms. [Preview Abstract] |
Tuesday, March 22, 2011 2:42PM - 2:54PM |
L31.00002: Pressure-induced Metallization of Carbon Disulfide Ranganath Dias, Mathew Debessai , Choong-Shik Yoo We will report high pressure electrical resistivity measurements on solid CS$_{2}$ in diamond anvil cell to 60GPa. The result shows a steady decrease in resistivity to that of metal at around 55GPa. Its visual appearance of CS$_{2}$ also supports its insulator-metal transition: the initially transparent CS$_{2}$ becomes opaque and eventually reflective with increasing pressure. We will also present a plausible mechanism for the observed metallization. [Preview Abstract] |
Tuesday, March 22, 2011 2:54PM - 3:06PM |
L31.00003: Electrical resistance measurement of optimal doped YBCO under pressure Takaki Muramatsu High pressure effect on nearly optimal doped high $T_{C}$ cuprate superconductor YBa$_{2}$Cu$_{3}$O$_{7-x}$ was studied by the electrical resistance measurements up to about 30 GPa. Superconducting phase of YBa$_{2}$Cu$_{3}$O$_{7-x}$ in pressure-temperature phase diagram was confirmed. $T_{C}$ has the broad maximum at about 8 GPa and then decreases with pressure and disappears at the pressure between 23 GPa and 25 GPa. In higher pressure region, the resistance shows upturn below about 60 K, indicating the possibility of crossover on YBa$_{2}$Cu$_{3}$O$_{7-x}$ from superconductor to semiconductor at about 24 GPa [Preview Abstract] |
Tuesday, March 22, 2011 3:06PM - 3:18PM |
L31.00004: Pressure induced phase transition in FeGa alloys Christopher DeVreugd, Muhtar Ahart, Peter Gehring, Dwight Viehland, Russell Hemley Giant magnetostriction in Fe-- x Ga alloys ( 15 -- x - 27 ) offers potential for future generations of sensors and actuators. A maximum in the magnetostrictive strain is found at Ga content of about 19 percent, which is ten times higher than that of pure alpha-Fe. To investigate the behavior of FeGa alloys under pressure, we chose a slow cooled alloy of FeGa-19 as our sample and performed x-ray diffraction experiments in a diamond anvil cell up to 45 GPa. Diffraction pattern shows powder rings associated with (110), (200), and (211) Bragg reflections from expected bcc structure of iron below 24 GPa. We also observed the intensity increases along the powder rings associated with the crystal structure of Galfenol. Considering the (110) Bragg peak splits into three peaks above 24 GPa, our results indicate that FeGa alloy undergoes a bcc cubic to a hexagonal transition around 24 GPa. When the pressure is decreased, the hcp phase transforms back to the bcc phase. The transition mechanism can be understood by using the analogy to the bcc-hcp phase transition in pure iron under pressure. The transition in iron is a martensitic or displacive one. The hcp structure can be derived from the bcc structure through a relatively minor distortion of the bcc structure. [Preview Abstract] |
Tuesday, March 22, 2011 3:18PM - 3:30PM |
L31.00005: High Pressure Studies of UO$_{3}$ Zsolt Jenei, Magnus Lipp, Jae-Hyun Klepeis, Bruce Baer, Hyunchae Cynn, William Evans, Changyong Park, Dimitri Popov It has been reported that upon compression t ambient temperature $\delta $-UO3 becomes amorphous at 2.2 GPa. (Journal of Alloys and Compounds 315 p59--61). We studied the properties of $\gamma $-UO3 in diamond anvil cell up to 75 GPa. Powder diffraction experiments performed at HPCAT/Advanced Photon Source show the crystalline uranium trioxide transforms to an amorphous solid between 12 and 14 GPa and remains amorphous up to 75 GPa. The transition has been confirmed by Raman spectroscopy as well. In this paper we'll present our findings on the amorphous transition together with the equation of state of both the crystalline phase and the amorphous phase. [Preview Abstract] |
Tuesday, March 22, 2011 3:30PM - 3:42PM |
L31.00006: High-pressure equation of state of U$_{3}$O$_{8}$ Jae-Hyun Klepeis, Zsolt Jenei, Magnus Lipp, William Evans, Dmitry Popov, Changyong Park We will present experimental studies at high pressures of the equation of state of U$_{3}$O$_{8}$. Isothermal pressure-volume measurements of U$_{3}$O$_{8}$ were made at ambient/elevated (600 K) temperatures in the pressure range of 1 atm $\sim$ 80 GPa (10 $\sim$ 70 GPa). Angle dispersive X-ray diffraction patterns at ambient temperature indicate that the A-centered orthorhombic structure of U$_{3}$O$_{8}$ transforms to the face centered cubic (fcc) structure above 9 GPa. Both the orthorhombic and cubic phases co-exist between 9 GPa and 30 GPa. As the temperature is increased at 10 GPa, we find that U$_{3}$O$_{8}$ also transforms to the fcc structure. As the pressure is increased at 600 K, the fcc structure undergoes a phase transition to the body centered tetragonal structure. Since the uranium in U$_{3}$O$_{8}$ is the dominant x-ray scatterer, the behavior of the oxygen at the phase transitions was measured using Raman spectroscopy. [Preview Abstract] |
Tuesday, March 22, 2011 3:42PM - 3:54PM |
L31.00007: High pressure x-ray diffraction of uranium oxide formed by natural oxidation of uranium Hyunchae Cynn, William J. Evans, Bruce J. Baer, Simon MacLeod, Magnus J. Lipp, Zsolt Jenei, J.H. Park Klepeis, Yue Meng, Stanislav Sinogeikin Naturally oxidized uranium has been compressed using a diamond anvil cell. Although X-ray diffraction shows the anisotropic nature in the pressure dependent changes to the lattice parameters of pure uranium as previously recorded, uranium oxide appears stable at high pressure in the fluorite structure with no clear evidence of a phase transition observed above the transition pressure previously measured for bulk uranium oxide. The lattice parameters of uranium oxide formed by natural surface oxidation have been determined along with those of the underlying pure uranium employing Rietveld refinement. We will discuss the seemingly unexpected findings about uranium oxide. [Preview Abstract] |
Tuesday, March 22, 2011 3:54PM - 4:06PM |
L31.00008: Uranium hydride (UH$_{3}$ ) and deuteride (UD$_{3}$) under conditions of high pressure and temperature Magnus Lipp, Zsolt Jenei, Jae Hyun Park Klepeis, Bruce Baer, Hyunchae Cynn, William Evans, Don Fujino, Blake Nolan, Joe Wermer, Changyong Park, Dmitry Popov Uranium hydrides are currently being evaluated as fuels in new reactor designs. They also serve as sources for very clean hydrogen by decomposing when heated at ambient pressure. We have examined their behavior over a large pressure and temperature range by placing small quantities and a pressure marker in a diamond anvil cell for angle dispersive x-ray diffraction. Neon was chosen as pressure transmitting medium to ensure the best possible hydrostatic conditions. We'll discuss crystal structures, the equation of state, the bulk modulus and the phase diagram. Work performed under the auspices of the US DOE by LLNL under Contract DE-AC52-07NA27344. Diffraction studies were performed at HPCAT (Sector 16), APS/ANL. HPCAT is supported by CIW, CDAC, UNLV and LLNL through funding from~DOE-NNSA, DOE-BES and NSF. APS is supported by DOE-BES, under Contract No. DE-AC02-06CH11357. [Preview Abstract] |
Tuesday, March 22, 2011 4:06PM - 4:18PM |
L31.00009: Structural Stabilities and Electronic Properties of Cobalt Hydrides Yasuyuki Matsuura, Tatsuya Shishidou, Tamio Oguchi Cobalt forms ferromagnetic hydrides CoH$_x$ at high pressures of hydrogen [1]. As the hydrogen pressure increases at temperatures 250-350${}^{\circ}$C, the concentration of hydrogen in the hcp phase monotonically increases, and reaches $x\sim 0.6$ at 7 GPa. At higher pressures, an fcc-based hydride with $x\sim 1.0$ is formed. At ambient pressure and 120 K, hydrogen atoms in the solution with $x\le 0.26$ are randomly distributed over octahedral interstitial sites [2]. In the solution with $x=0.34$ ($x\ge 0.38$), hydrogen atoms occupy every third (second) layer. The magnetic moments of the hcp-based hydrides are oriented to the $c$-axis, and are decreased with increasing hydrogen concentration at a rate of about 0.36 $\mu_{\mathrm{B}} $ per hydrogen atom. In this study, we optimize the structural parameters for several structures, and investigate the structural stabilities and related electronic properties by using first-principles calculations. The full-potential linearized augmented plane wave method with the generalized gradient approximation is adopted.\\[4pt] [1] V. E. Antonov, J. Alloys Compd. \textbf{330}-\textbf{332}, 110 (2002).\\[0pt] [2] V. K. Fedotov, V. E. Antonov, T. E. Antonova, E. L. Bokhenkov, B. Dorner, G. Grosse, and F. E. Wagner, J. Alloys Compd. \textbf{291}, 1 (1999). [Preview Abstract] |
Tuesday, March 22, 2011 4:18PM - 4:30PM |
L31.00010: Formation of collapsed tetragonal phase in EuCo$_{2}$As$_{2}$ under high pressure Matthew Bishop, Walter Uhoya, Georgiy Tsoi, Yogesh Vohra, Athena Sefat, Brian Sales The structural properties of EuCo$_{2}$As$_{2}$ have been studied up to 35 GPa, through the use of x-ray diffraction in a diamond anvil cell at a synchrotron source. At ambient conditions, EuCo$_{2}$As$_{2}$ ($I$4/\textit{mmm}) has a tetragonal lattice structure with a bulk modulus of 48 $\pm $ 4 GPa. With the application of pressure, the $a $axis exhibits negative compressibility with a concurrent sharp decrease in $c$-axis length. The anomalous compressibility of the $a $axis continues until 4.7 GPa, at which point the structure undergoes a second-order phase transition to a collapsed tetragonal (CT) state with a bulk modulus of 111 $\pm $ 2 GPa. We found a strong correlation between the ambient pressure volume of 122 parents of superconductors and the corresponding tetragonal to collapsed tetragonal phase transition pressures. [Preview Abstract] |
Tuesday, March 22, 2011 4:30PM - 4:42PM |
L31.00011: The behavior of semi-metal Bi$_{4}$Te$_{3}$ under pressure Jason Jeffries, A.L. Lima Sharma, P.A. Sharma, C.D. Spataru, S.K. McCall, J.D. Sugar, S.T. Weir, Y.K. Vohra As a member of the (Bi$_{2})_{m}$(Bi$_{2}$Te$_{3})_{n}$ adaptive series, Bi$_{4}$Te$_{3}$ exhibits identical crystallographic symmetry and similar electronic properties to the archetypal thermoelectric material Bi$_{2}$Te$_{3}$. The extra Bi atoms in Bi$_{4}$Te$_{3}$ serve to increase the electronic density of states, making Bi$_{4}$Te$_{3}$ a semi-metal, as opposed to semiconducting Bi$_{2}$Te$_{3}$, at ambient pressure. We will report the results of high-pressure structural and magnetotransport characterization of Bi$_{4}$Te$_{3}$, focusing on the interplay between structural parameters and the underlying electronic properties. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344. [Preview Abstract] |
Tuesday, March 22, 2011 4:42PM - 4:54PM |
L31.00012: Theoretical X-ray Spectroscopy for Strongly Correlated Materials at High Pressure Adam P. Sorini, Cheng-Chien Chen, Shibing Wang, Wendy L. Mao, Thomas P. Devereaux, Chi-Chang Kao We present theoretical x-ray spectra for correlated d- and f-electron materials under extreme conditions. We use exact-diagonalization to study small clusters of atoms including ligand charge-transfer and atomic-multiplet effects. These techniques allow us to extract information from spectroscopic measurements regarding phase transitions in strongly correlated materials as a function of pressure. We show recent results for hematite (Fe2O3) which undergoes a variety of phase transitions (structural, spin, metal/insulator) near 50 GPa, which have been observed using hard x-ray quadrupolar absorption. We also apply our models to the correlated f-electron ``volume collapse" systems which show complex behavior under pressure. [Preview Abstract] |
Tuesday, March 22, 2011 4:54PM - 5:06PM |
L31.00013: Fermi surface of SnO under pressure Niels Christensen, Axel Svane Tin monoxide undergoes a pressure induced insulator-metal transition around 5 GPa. The pressure effects on the electronic band structure, the Fermi surface (FS) and its nesting properties of SnO in the metallic phase have been derived from ab initio calculations within the local density (LDA) and quasiparticle selfconsistent GW (QSGW) approximations. It is found that the topologies of the FS determined by the two approaches are very similar. Nesting occurs between two different sheets of the FS, most pronounced via (1,1,0) Q- vectors connecting the outer electron surface with the hole surface The present study was motivated by recent observation of superconductivity in SnO under pressure [1]. \\[4pt] [1] M.K. Forthaus el al., Phys. Rev. Lett. {\bf 105}, 157001 (2010). [Preview Abstract] |
Tuesday, March 22, 2011 5:06PM - 5:18PM |
L31.00014: Dynamic response of Cu46Zr54 metallic glass to high-strain-rate shock loading: Plasticity, spall, and atomic-level structures Bedri Arman, Sheng-Nian Luo, Timothy Germann, Tahir Cagin Dynamic response of Cu46Zr54 metallic glass under adiabatic planar shock wave loading with molecular dynamics simulations was investigated. We analyzed the Hugoniot (shock) states up to 60 GPa, shock-induced plasticity and dynamic spall strengths. Especially, the spall strengths likely represent the limiting values achievable in experiments such as laser ablation. To characterize local deformation and structure at various stages of shock, release, tension and spallation, the local von Mises shear strain and Voronoi tessellation analyses were used. Modeled glass showed plasticity as localized shear transformation zones rather than thermal origin. Nucleation of voids occurred preferentially at the highly shear-deformed regions. Our simulations through the Voronoi and shear strain analyses suggest that the atoms having different local structures are of different shear resistances that lead to shear localization. [Preview Abstract] |
Tuesday, March 22, 2011 5:18PM - 5:30PM |
L31.00015: Single Crystal X-ray Diffraction at Megabar Pressures and Temperatures of Thousands Degrees Leonid Dubrovinsky, Natalia Dubrovinskaia, Marco Merlini, Michael Hanfland The most reliable information about crystal structures and their response to changes in pressure and temperature is obtained from single crystal diffraction experiments. We have developed a methodology to perform single crystal X-ray diffraction experiments in laser-heated diamond anvil cells and demonstrate that structural refinements and accurate measurements of the thermal equation of state of metals, oxides, silicates from single crystal intensity data are possible in a pressures ranging up to megabars and temperatures of thousands degrees. New methodology was applied to solve \textit{in situ} high-pressure high-temperature structure of iron oxide and study structural variations of iron and aluminum bearing silicate perovskite at conditions of the Earth lower mantle. [Preview Abstract] |
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