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 E2: CM.2 Phase Transitions: Melting |
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Chair: Nenad Velisavljevic, Los Alamos National Laboratory Room: Grand Ballroom II |
Monday, July 8, 2013 3:30PM - 4:00PM |
E2.00001: Melting curve of metals evidenced by X-ray diffraction Invited Speaker: Agnes Dewaele There has been a consistent pattern of disagreement between the determinations of high pressure melting by two experimental techniques, the static laser-heated diamond anvil cell (LHDAC) and the dynamic shock wave compression. For several elements, ``high'' and ``low'' melting points have been measured by shock compression and LHDAC, respectively. The difference could exceed one thousand of K. We have re-visited the melting curve of a few metals in a LHDAC: lead, tantalum, beryllium and iron. We have used an alternative diagnostic of melting, based on X-ray diffraction instead of optical detection. The melting curves obtained with this diagnostic are in correct agreement with shock wave data. Movements of the sample surface, which were previously interpreted as a melting signature, could be due to a fast recrystallization of the solid sample. This fast recrystallization is evidenced by X-ray diffraction up to several hundreds of degrees below melting for some metals. [Preview Abstract] |
Monday, July 8, 2013 4:00PM - 4:15PM |
E2.00002: Guest Chain ``Melting'' in Incommensurate Host-Guest Potassium Emma McBride, Keith Munro, Malcolm McMahon Upon increasing pressure the group-I elements transform from close-packed structures (\textit{bcc} and \textit{fcc}) to a series of low-symmetry complex structures. Residing in the middle of the group, potassium (K) has numerous structures in common with its neighbours, and, in fact, is remarkably structurally similar to sodium (Na) and rubidium (Rb). For example, the post-\textit{fcc} transition in K is to a composite incommensurate host-guest structure (\textit{tI}19), and the host structure of this phase is isostructural with that found in Na and Rb. Previously we have reported that below 16.7GPa, the Bragg peaks from the guest component of \textit{tI}19--Rb broaden considerably, signalling a loss of the inter-chain correlation, or a ``melting'' of the chains. Furthermore, in \textit{tI}19-Na above 125 GPa, the Bragg peaks from the guest component are also broadened, suggesting that the guest chains are also nearly ``melted.'' During studies of the melting curve of K, we observed that the guest peaks from \textit{tI}19-K broaden dramatically on heating. Here we report single-crystal, quasi-single-crystal, and powder synchrotron x-ray diffraction measurements of \textit{tI}19-K to 50~GPa and 800 K, which allowed a detailed study of this chain ``melting'' transition. The order-disorder transition is clearly visible over a 30 GPa pressure range, and there are significant changes in the gradient of the phase boundary, which may be influenced by the nature of the guest structure. Furthermore, data extending the melting curve will also be presented. [Preview Abstract] |
Monday, July 8, 2013 4:15PM - 4:30PM |
E2.00003: Melting of lithium at high pressure Shanti Deemyad, Anne Marie Schaeffer At ambient pressure, lithium is the lightest metallic element and the prototype of a simple metal, with a nearly spherical Fermi surface. The structural and electronic properties of lithium at high densities are highly counterintuitive. Under high pressure, lithium undergoes a series of symmetry breaking structural phase transitions and a theoretically predicted complex melting curve. In addition, because of its low atomic mass, lithium may behave as a quantum solid. If this is the case, its melting transition would resemble that of metallic hydrogen, and is of critical interest. Direct observation of the melting transition of lithium under high pressure has been challenging due to its strong reactivity. In this talk I will review the unusual physics of lithium at extreme pressures and present our recent experimental result on high pressure melting curve of lithium. [Preview Abstract] |
Monday, July 8, 2013 4:30PM - 4:45PM |
E2.00004: High pressure melting of lithium Anne Marie Schaeffer, William Talmadge, Scott Temple, Shanti Deemyad The electrical resistivity of metals exhibit a well documented sharp increase near the melting temperature. The electrical resistivity of lithium was measured using a quasi-four point probe inside a diamond anvil cell. The sharp increase in the resistivity upon melting, complemented by visual observations, was used to measure the melting curve of lithium from ambient pressure to 64 GPa. Using the same experimental configuration, the electrical resistivity measurements of lithium have been expanded. [Preview Abstract] |
Monday, July 8, 2013 4:45PM - 5:00PM |
E2.00005: Dynamic Melting of Highly Compressed Nitrogen Dane Tomasino, Choong-Shik Yoo Nitrogen exhibits a fascinating high-pressure polymorphism in solid along with the predicted transition to a conducting polymer in liquid. The solid-liquid phase boundary, however, is still the subject of debate -- not well understood. This is, in part, due to a lacking of proper in-situ structural/chemical diagnostic technique capable of probing hot dense nitrogen phases at high pressures and temperatures. The challenge is mainly due to high mass and thermal diffusivity and chemical reactivity of hot dense fluids. To remedy this situation, we have applied the time-resolved Raman spectroscopy on laser-heated nitrogen in diamond anvil cells. In this experiment, the onset of melting was determined in-situ by probing the discontinuous spectral change in nitrogen vibrons during rapid isochoric heating, while the temperature was measured through time-resolved thermal spectro-radiometry. [Preview Abstract] |
Monday, July 8, 2013 5:00PM - 5:15PM |
E2.00006: Atomistic modeling of graphite melting Nikita Orekhov, Vladimir Stegailov Graphite melting properties have been the subjects of debate for many years due to discrepancy in experimental data. We report here molecular dynamic simulations of graphite melting with the semiepirical bond-order potential AIREBO. As a result in the pressure range up to 14 GPa the graphite melting line was obtained and properties of liquid carbon were investigated. For the superheated graphite the melting front velocity dependencies on temperature were calculated to verify the values of melting temperatures. [Preview Abstract] |
Monday, July 8, 2013 5:15PM - 5:30PM |
E2.00007: Melting of GaN -- still open problem S. Porowski, B. Sadovyi, S. Gierlotka, A. Presz, I. Grzegory, I. Petrusha, V. Turkevich, D. Statiichuk In this work, thermal stability of GaN single crystals at pressure up to 9.0~GPa and temperature up to 3400~K has been studied. According to [1] the congruent melting of GaN occurs at 2533~K at pressure above 6.0~GPa. Results obtained in our study are not in agreement with this observation. In whole pressure and temperature range we observed that GaN decomposes to N$_{2}$ gas and liquid gallium solution of nitrogen. The p-T decomposition curve which has been established is consistent with previously reported data for lower pressures and temperatures [2]. Also corresponding solubility of nitrogen in the liquid gallium has been evaluated by measuring the weight of crystals grown from solution at cooling of the system. At the highest pressure 17~at.~{\%} solubility was observed which is still significantly lower than 50~at.~{\%} required for stoichiometric melt. \\[4pt] [1] W.~Utsumi et al. Nature Materials \textbf{2}, 735 (2003).\\[0pt] [2] J. Karpi\'{n}ski et al. J. Crystl Growth \textbf{66}, 1 (1984). [Preview Abstract] |
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