Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session G40: Matter in Extreme Environments I: Advanced ExperimentsFocus
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Sponsoring Units: DCOMP DMP Chair: Xiaoyu Wang Room: 705 |
Tuesday, March 3, 2020 11:15AM - 11:51AM |
G40.00001: On the Dynamic Compression of Elements: Phase Transition Lowering in Dynamically-Compressed Silicon Invited Speaker: Emma McBride Despite being the subject of numerous shock compression studies, the behavior of silicon under dynamic loading is vigorously debated [1-4]. The few studies that combine shock compression and X-ray diffraction have exclusively focused on "normal" X-ray geometry whereby X-rays are collected along the shock propagation direction, consequently sampling numerous strain states at once, and hence greatly complicating both phase identification and studies of phase transition kinetics.[5] Here, we present a novel setup to perform in situ X-ray diffraction studies perpendicular to the shock propagation direction at the Matter in Extreme Conditions end station at Linac Coherent Light Source, SLAC. Combining the extremely bright, micro-focused X-ray beam available at the LCLS with a nanosecond laser driver, we unambiguously characterize of the complex multi-wave shock response in silicon for the first time. We further combine this platform with simultaneous imaging with diffraction from shock compressed germanium. |
Tuesday, March 3, 2020 11:51AM - 12:03PM |
G40.00002: Laser shock induced insulator-metal transition in quasi-one dimensional single-component radical Yong Hu, Shenqiang Ren Laser shock is a relatively new surface treatment for high pressure study[1]. The shock waves can create over one hundred GPa transient shock pressure[2]. Here we found the laser shock induced revisable insulator-metal transition in single-component radical, K-TCNQ[3], where the effect of antiferromagnetic spin ordering causes insulating behavior. The manipulation of spin exchange interaction with external laser shock wave, electric field and magnetic field is accompanied by insulator to metal transition, gigantic magnetoelectric and magneto capacitance effects. One dimensional systems therefore provide a new area to search for conducting magnetoelectric media. |
Tuesday, March 3, 2020 12:03PM - 12:15PM |
G40.00003: Overview of High Pressure Collaborative Access Team (HPCAT) facility at the Advanced Photon Source at Argonne National Laboratory Nenad Velisavljevic, Maddury Somayazulu HPCAT is a dedicated facility for high pressure research and is located within the Advanced Photon Source. Goal of HPCAT is to develop and implement synchrotron-based x-ray techniques that are coupled with diamond anvil cell, portable large volume press, and other platforms for studying materials at extreme pressure-temperature conditions. |
Tuesday, March 3, 2020 12:15PM - 12:51PM |
G40.00004: Crystal Structure and Reflectivity of Laser Ramp-Compressed Sodium Invited Speaker: Danae Polsin Extreme compression can alter the free-electron behavior of “simple” metals such as sodium. At pressures exceeding 200 GPa, Na was observed to become transparent to visible light under static compression. First-principles calculations suggest this is caused by a transformation to an electride phase where electrons are localized in interstitial positions. Laser-driven ramp compression is used to compress Na into an unexplored pressure regime to investigate the crystalline structure, reflectivity, and melting behavior. X-ray diffraction is used to constrain the crystalline structure and detect melting. Optical reflectivity measurements at 532 nm are used to detect a transition to the observed insulating electride phase. We show the highest-pressure solid x-ray diffraction and reflectivity data on Na to date. The results indicate the Na phase diagram is more complicated than predicted by zero-temperature DFT. |
Tuesday, March 3, 2020 12:51PM - 1:03PM |
G40.00005: Neutron Scattering Research on Quantum Materials under Pressure Antonio dos Santos Quantum Materials are characterized by an extreme sensitivity to weak external perturbations (H, E, P). Among these, pressure is unique in that, even in a moderate range, it induces structural changes energetically equivalent to thousands of K. In addition, samples subjected to pressure do not suffer from chemical segregation or disorder, characteristic of chemical manipulation. In this context, neutron scattering, with its ability to inspect simultaneously the lattice and spin degrees of freedom, while not depositing any energy, is uniquely suitable for the study of quantum systems. Instruments at modern neutron sources, such as the spallation neutron source, are now fitted with custom made pressure devices, that extend the realm of the possible in neutron scattering of the quantum world. Indeed, the range of pressure, temperature and field available, allow faster measurements on smaller samples. Here we will present the current suite of instrumentation available to research of quantum materials at the SNS, including new developments in instrumentation and pressure devices. These advances will be illustrated with science examples that benefited from these new capabilities. |
Tuesday, March 3, 2020 1:03PM - 1:15PM |
G40.00006: Magnetic Structure of the High-Pressure Phases of Holmium Christopher Perreault, Yogesh Vohra, Antonio Moreira Dos Santos, Jamie Molaison The magnetic phases in rare earth metals are well established under ambient pressure conditions, however, little is known about the magnetic ordering in their corresponding high pressure crystalline modifications. Holmium (Ho) was studied in a large-volume diamond anvil cell at the Spallation Neutron Source to 20 GPa and 10 K. The ambient pressure hexagonal close packed phase (hcp) of holmium shows two magnetic transitions below 10 GPa one to Antiferromagnetic (AFM) incommensurate phase and another to a Ferromagnetic (FM) phase. At pressures above 10 GPa, Ho transforms to the alpha-Samarium (α-Sm) phase which shows only one transition marked by appearance of a magnetic peak at 3 Å below 20 K that is more intense than the nuclear peaks. This magnetic order remains even when pressure is increased past 19 GPa where the sample again transforms, this time to the double hexagonal close packed (dhcp) phase. The magnetic ordering temperature increases with pressure from below 20 K at 15 GPa to around 25 K at 20 GPa. The magnetic phase diagram of Ho is presented to 20 GPa and 10 K. |
Tuesday, March 3, 2020 1:15PM - 1:27PM |
G40.00007: Lattice Dynamics of Highly Porous Materials Matthew Ryder Highly porous materials such as MOFs, COFs and HOFs have been shown to have promising electronic and dielectric properties.1-3 However, high levels of porosity often couple with low structural stability.4,5 Therefore, the collective lattice dynamics reveal a diversity of valuable information relating to the structural flexibility and the mechanistic origins of anomalous mechanical phenomena.6-8 Spectroscopic techniques such as inelastic neutron scattering (INS), in conjunction with DFT, are used to study the phonon mode dynamics, including those related to gate opening and breathing,6 trampoline-like mechanisms and molecular rotors reminiscent of negative thermal expansion (NTE),7,8 and buckling of 2D layers.9 The work has also revealed the effect of external stimuli (pressure and temperature) and shown stimuli-induced phase transitions and amorphization.9-11 |
Tuesday, March 3, 2020 1:27PM - 2:03PM |
G40.00008: Impact-induced chemistry and physics through high-energy ball milling Invited Speaker: Przemyslaw Dera Mechanochemical activation by high-energy milling has become a widely used method for solid state synthesis, and alternative to high-temperature processes. It has been successfully used for synthesis of crystalline and amorphous alloys, intermetallic compounds, metastable phases, nanomaterials and metal-ceramic composites. Mechanochemical synthesis utilizes high-energy impact phenomena to initiate chemical reactions or structural phase transitions. The peak impact pressures which the individual sample particles experience vary depending on the type of mill, milling speed, as well as size, shape and density of the attritor components, but can reach 20 GPa, while the temperature typically remains below 100C. Remarkably, this is achieved with significant sample quantities (grams), over a short period of time, and very inexpensively. Whereas mechanisms and kinetics of solid-state reactions induced by temperature or static pressure are fairly well understood, transformations of materials under continuous impact in a milling assembly remain largely unexplored and are based almost exclusively on ex situ studies. During the mechanical activation particles undergo heavy deformation and experience significant strains. This results in formation of a variety of crystal defects such as dislocations, vacancies, stacking faults and increased number of particle boundaries, making the milled material energetically less stable. An on-going project at the PX2 synchrotron beamline will adapt the in situ real-time X-ray diffraction monitoring of structural and chemical changes during the milling process. This presentation will also introduce a new project to develop more economical mechanochemical paths towards synthesis of the cubic phase of boron nitride. |
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