Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session Z3: CM Condensed Matter: Lanthanides and Actinides |
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Chair: Tony Zocher, Los Alamos National Laboratory Room: Fifth Avenue |
Friday, July 12, 2013 11:00AM - 11:15AM |
Z3.00001: Cerium under High Pressure (and Temperature): X-ray Diffraction and Emission, Radiography and Ultrasound Magnus Lipp, Zsolt Jenei, Hyunchae Cynn, William Evans, Paul Chow, Yuming Xiao, Yoshio Kono, Curtis Kenney-Benson Modern experimental techniques have increased our knowledge of cerium's unique behavior under the elements, an iso-structural (fcc) volume collapse transition of 15{\%} at room temperature from the $\gamma $- to the $\alpha $-phase ending in a critical point. Our recent findings favor a Kondo Volume Collapse model, a step-wise decrease of the moment across the transition but then continuation of most of it. Simple radiography appears to tell us that both solid phases continue on in some form into the liquid. The contribution of the lattice-phonons to this transition is re-evaluated using a unique combination of several techniques eliminating any indirect / iterative procedures. This methodology provides new data about the elastic properties bridging the gap from the atomic to the meso-scale dimension. Our preliminary analysis indicates a larger contribution by the lattice phonons as very recently thought. This work was performed under the auspices of the US DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The X-ray 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] |
Friday, July 12, 2013 11:15AM - 11:30AM |
Z3.00002: Experimental Investigation of Dynamic Compression and Spallation of Cerium at Pressures up to 6 GPa Alla Zubareva, Sergey Kolesnikov, Alexander Utkin In this study the experiments on one-dimensional dynamic compression of Cerium (Ce) samples to pressures of 0.5 to 6 GPa through an impact of Al flyer plates accelerated with various types of explosively driven generators were conducted. VISAR laser velocimeter was used to obtain Ce free surface velocity profiles. At pressures of about 0.5 GPa the isentropic compression wave which was blurred in time was registered instead of a usual shock wave. It was due to the anomalous compressibility of $\gamma $-phase of Ce. At pressures higher than 0.78 GPa that corresponded to $\gamma $-$\alpha $-transition in Ce the two-wave configuration was observed which consisted of the similar wave of isentropic compression and the following shock jump. At the profiles obtained for experiments with thin Al flyer plates a shock rarefaction wave was clearly registered in Ce samples, the appearance of which was also due to the anomalous compressibility of $\gamma $-phase. In several samples spall phenomena were also observed. The results showed a strong dependence of the spall strength of Ce on the strain rate: at its increase by an order of magnitude (3*10$^{\mathrm{4\thinspace }}$to 3*10$^{\mathrm{5}}$ s$^{\mathrm{-1}})$ the spall strength rose from 0.4 to 0.6 GPa. Authors would like to thank M.V. Zhernokletov for supplied samples. [Preview Abstract] |
Friday, July 12, 2013 11:30AM - 11:45AM |
Z3.00003: Pressure-induced iso-structural phase transition in CeO$_{2}$ above megabar pressures Lei Liu, Wenge Yang, Hongxing Song, Huayun Geng, Yan Bi, Jian Xu The pressure-induced structural phase transition of cerium dioxide, CeO$_{2}$, has been studied by synchrotron angle X-ray diffraction technique using diamond anvil cell up to 175 GPa at room temperature. In addition to the \textit{Fm-3m} to \textit{pnma} structural phase transition at about 30 GPa, which was found previously, a \textit{pnma} to\textit{ pnma} iso-structural phase transition was found above megabar pressure range. During the phase transition, the $a$ axis of the unit cell collapses, while the $b$ and $c$ axis expand. However, abrupt change of the unit cell volume during the phase transition was not observed. [Preview Abstract] |
Friday, July 12, 2013 11:45AM - 12:00PM |
Z3.00004: Neutron Diffraction and Electrical Transport Studies on Magnetic Transition in Terbium at High Pressures and Low Temperatures Sarah Thomas, Jeffrey Montgomery, Georgiy Tsoi, Yogesh Vohra, Samuel Weir, Christopher Tulk, Antonio Moreira Dos Santos Neutron diffraction and electrical transport measurements have been carried out on the heavy rare earth metal terbium at high pressures and low temperatures in order to elucidate its transition from a helical antiferromagnetic to a ferromagnetic ordered phase as a function of pressure. The electrical resistance measurements using designer diamonds show a change in slope as the temperature is lowered through the ferromagnetic Curie temperature. The temperature of the ferromagnetic transition decreases at a rate of -16.7 K/GPa till 3.6 GPa, where terbium undergoes a structural transition from hexagonal close packed (hcp) to an $\alpha $-Sm phase. Above this pressure, the electrical resistance measurements no longer exhibit a change in slope. In order to confirm the change in magnetic phase suggested by the electrical resistance measurements, neutron diffraction measurements were conducted at the SNAP beamline at the Oak Ridge National Laboratory. Measurements were made at pressures to 5.3 GPa and temperatures as low as 90 K. An abrupt increase in peak intensity in the neutron diffraction spectra signaled the onset of magnetic order below the Curie temperature. A magnetic phase diagram of rare earth metal terbium will be presented to 5.3 GPa and 90 K based on these studies. [Preview Abstract] |
Friday, July 12, 2013 12:00PM - 12:15PM |
Z3.00005: Origin of the Pressure-Induced Volume Collapse in Tb Gilberto Fabbris, Jinhyuk Lim, Jose Renato Mardegan, Daniel Haskel, James Schilling The mechanism responsible for the high-pressure volume collapse in most elemental rare-earth metals is still a matter of debate. Models attempting to explain this collapse include: (i) valence transition, (ii) 4$f$ local-to-band transition (Mott-Hubbard), (iii) $f$-$d$ hybridization (Kondo), and (iv) \textit{sp}$\to d$ transfer. We focus on Tb metal which displays a 5{\%} volume collapse at 53 GPa. X-ray absorption spectroscopy shows persistence of Tb's 4$f^{\mathrm{8}}$ state across the volume collapse, excluding (i) as a mechanism. Furthermore, x-ray emission spectroscopy shows that 4$f$ states retain their localized nature to at least 70 GPa, ruling out (ii). On the other hand, the suppression of the x-ray absorption ``white line'' with pressure indicates that \textit{sp}$\to d$ transfer is active. To probe for Kondo interactions, the pressure dependence of the superconducting $T_{\mathrm{c}}$ in pure Y is compared to that in a Y(0.5 at{\%} Tb) alloy. We observe a strong suppression of $T_{\mathrm{c}}$ at pressures near terbium's volume collapse, an indication of a rapid increase of the Kondo temperature, in agreement with (iii). We argue that a Kondo model in the presence of \textit{sp}$\to d$ transfer best describes the volume collapse in Tb metal. [Preview Abstract] |
Friday, July 12, 2013 12:15PM - 12:30PM |
Z3.00006: Phase Transformation of U$_{3}$O$_{8}$ and Enhanced Structural Stability at Extreme Conditions Fuxiang Zhang, Maik Lang, Rodney Ewing A powder sample of $\beta $-U$_{3}$O$_{8}$ was pressurized at room temperature up to 37.5 GPa with a symmetric diamond anvil cell. XRD patterns clearly indicated that a phase transition occurred between 3-11 GPa. The high-pressure phase is a fluorite-like structure. The fluorite-like structure is stable up to 37.5 GPa. The high-pressure phase was then laser heated to over 1700 K in the diamond anvil cell at high pressure conditions. No phase transition was found at high pressure/ temperature conditions, and the fluorite-like structure of U$_{3}$O$_{8}$ is even fully quenchable. The lattice parameter of the fluorite-like high-pressure phase is 5.425 {\AA} at ambient conditions, which is smaller than that of the stoichiometric UO$_{2}$. Previous experiments have shown that the stoichiometric uranium dioxide (UO$_{2})$ is not stable at high pressure conditions and starts to transform to a cotunnite structure at $\sim$30 GPa. When heating the sample at high pressure, the critical transtion pressure is greatly reduced. However, the fluorite-like high-pressure phase of U$_{3}$O$_{8}$ is very stable at high pressure/high temperature conditions. The enhanced phase stability is believed to be related to the presence of extra oxygen (or U vacancies) in the structure. [Preview Abstract] |
Friday, July 12, 2013 12:30PM - 12:45PM |
Z3.00007: Complex Structural Phase Transitions in Europium at High Pressure Rachel Husband, Ingo Loa, Malcolm McMahon Europium (Eu), which is divalent at ambient pressure due to its half-filled 4f electron shell, is an anomalous element in the lanthanide series, in which the majority of the elements are trivalent. Consequently, Eu does not fit in with the general trend of structural phase transitions observed in the trivalent lanthanide elements, and its behaviour is much more complex. The Eu-IV phase, stable above 31.5 GPa, is the only known incommensurate structure in the lanthanide series$^{\mathrm{1}}$. Early spectroscopic measurements indicated that the valence of Eu increases continuously under pressure$^{\mathrm{2}}$, but a recent study concluded that Eu remains nearly divalent up to 87~GPa$^{\mathrm{3}}$. We will present the results of our x-ray diffraction studies of Eu up to a pressure of 100 GPa, well into the superconducting region. Initial structural studies were greatly complicated by the presence of two pressure-induced contaminant phases$^{\mathrm{4,\thinspace 5}}$, and so great care was taken to obtain `clean' samples. We will report a transition to a second incommensurately-modulated phase, Eu-V, above 42~GPa. This transition is accompanied by an increase in modulation amplitudes and the appearance of higher-order satellite reflections, suggesting a complex modulation wave. This is the first pressure-induced incommensurate-incommensurate (non-host-guest) transition to be observed in the elements at high pressure. $^{\mathrm{1}}$Husband \textit{et al. }Phys. Rev Lett. \textbf{109,} 095503 (2012). $^{\mathrm{2}}$R\"{o}hler, Physica B$+$C \textbf{144}, 27 (1986). $^{\mathrm{3}}$Bi \textit{et al.}, Phys. Rev. B. \textbf{85}, 205134 (2012). $^{\mathrm{4}}$Husband \textit{et al.}, J Phys Conf Ser. \textbf{377}, 012030 (2012). $^{\mathrm{5}}$Husband \textit{et al.}, High Press. Res. (in Press). [Preview Abstract] |
Friday, July 12, 2013 12:45PM - 1:00PM |
Z3.00008: On structural, elastic and dynamic stability of rare earth nitrides: First principle calculations B.D. Sahoo, K.D. Joshi, S.C. Gupta The structural stability of LaN and CeN under hydrostatic compression has been analysed theoretically. For LaN the comparison of enthalpies calculated at various pressures for rocksalt type (B1), tetragonal (B10) and CsCl type (B2) structures suggests that the B1 phase will transform to B10 structure at $\sim$ 20 GPa, in line with the experimental value of 22.8 GPa. Additionally, we predict the B10 to B2 phase transition at higher pressure of $\sim$ 165 GPa. Similar transition sequence has been predicted for CeN also with the B1 to B10 and B10 to B2 transition pressures calculated as 53 GPa and 198 GPa, respectively. However, the static high pressure EDXRD measurements on CeN by Olsen et al. report direct B1 to B2 phase transition at $\sim$ 65 GPa. To resolve this discrepancy, we have performed lattice dynamic calculations on these structures. The phonon spectra calculated at zero pressure correctly shows B1 phase to be dynamically stable and B10 and B2 to be unstable. At 65 GPa the B1 phase becomes dynamically unstable and the B10 emerges as a dynamically stable phase whereas B2 still remains unstable, supporting theoretical finding. Further, our results are substantiated by calculated ADXRD pattern of B10 and B2 phases. [Preview Abstract] |
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