Wednesday, August 24, 11:30AM, BPB 217
Assessing zeolite frameworks for noble gas separations through a joint experimental and computational approach
Grand canonical Monte Carlo is a simulation methodology to statistically analyze the thermodynamics of a system and evaluate a equilibrium guest-host properties of a system. All 229 currently identified zeolite frameworks are screened in their siliceous form by grand canonical Monte Carlo simulation for their ability to separate a radiochemically relevant Kr/Xe mixture in a pressure swing adsorption process. Prior to screening, our model was benchmarked against experimental single gas adsorption measurements, and it was found that for Kr and Xe a Lennard-Jones 9-6 potential with a softer repulsion than an equivalently parameterized Lennard-Jones 12-6 potential was necessary to accurately model fluid-fluid interactions. We examined the most promising candidate materials and made conclusions about which pore geometries work best for the separation. We also performed gas adsorption experiments on an AlPO material to test the transferability of our siliceous results. We will also discuss extensions of this project to utilize hybrid simulation techniques to model gas adsorption and trapping at high pressure conditions.
Thurday, August 25, 11:30AM, BPB 217
Novel chemistry under high pressure
Maosheng Miaoa,b +
a Department of Chemistry and Biochemistry, California State University Northridge
b Beijing Computational Science Research Center, Beijing, China
The chemistry at ambient condition has implicit boundaries rooted in the atomic shell structure: the inner-shell electrons and the unoccupied outer-shell orbitals do not involve as major component in chemical reactions and in chemical bonds. The chemical properties of atoms are determined by the electrons in the outermost shell; hence, these electrons are called valence electrons. These general rules govern our understanding of chemical structures and reactions.
Using first principles calculations, we demonstrate that under high pressure, the above doctrines can be broken. We show that both the inner shell electrons and the outer shell empty orbitals of Cs and other elements can involve in chemical reactions. In the presence of fluorine and under pressure, the formation of CsFn (n > 1) compounds containing neutral or ionic molecules is predicted. Their geometry and bonding resemble that of isoelectronic XeFn molecules, showing a caesium atom that behaves chemically like a p-block element under these conditions. Furthermore, we find that under high pressure Hg in Hg-F compounds transfers charge from the d orbitals to the F, thus behaving as a transition metal. Oxidizing Hg to + 4 and + 3 yielded the thermodynamically stable compounds HgF4 and HgF3. The former consists of HgF4 planar molecules. HgF3 is metallic and ferromagnetic, with a large gap between its partially occupied and unoccupied bands under high pressure.
In other works, we find that Xe, Kr, and Ar can form thermodynamically stable compounds with Mg at high. The resulting compounds are metallic and the noble gas atoms are negatively charged, suggesting that chemical species with a completely filled shell can gain electrons, filling their outermost shell(s). Similarly, we predicted that pressure can cause large electron transfer from light alkali metals such as Li to Cs, causing Cs to become anionic with a formal charge much beyond -1.
Furthermore, we show that the quantized orbitals of the enclosed interstitial space may play the same role as atomic orbitals, an unprecedented view that led us to a unified theory for the recently observed high-pressure electride phenomenon .
+ Author for correspondence: firstname.lastname@example.org
- M. S. Miao, Nature Chemistry, 5, 846 (2013).
- J. Botana, X. Wang, C. Hou, D. Yan, H. Lin, Y. Ma and M. S. Miao, Angew. Chemie 54, 9280-9283 (2015).
- M. S. Miao, X. L. Wang, J. Brgoch, . Spera, M. G. Jackson, G. Kresse, and H. Q. Lin, J. Am. Chem. Soc. 137, 14122 (2015)
- J. Botana and M. S. Miao, Nature Communications, 5, 4861 (2014).
- M. S. Miao and R. Hoffmann, Accounts of Chemical Research, 47, 1311 (2014).
Wednesday, August 17, 11:30AM, BPB 217
Encapsulation kinetics and dynamics of carbon monoxide in clathrate hydrate
Abstract:Carbon monoxide clathrate hydrate is a potentially important constituent in the solar system. In contrast to the well-established relation between the size of gaseous molecule and hydrate structure, previous work showed that carbon monoxide molecules preferentially form structure-I rather than structure-II gas hydrate. Resolving this discrepancy is fundamentally important to understanding clathrate formation, structure stabilization and the role the dipole moment/molecular polarizability plays in these processes. Here we report the synthesis of structure-II carbon monoxide hydrate under moderate high-pressure/low-temperature conditions. We demonstrate that the relative stability between structure-I and structure-II hydrates is primarily determined by kinetically controlled cage filling and associated binding energies.
Wednesday, August 3, 11:30AM, BPB 217
Synthesis, Characterization, and Properties Study of Superhard Diamond-cBN Alloy
Diamond and cubic boron nitride (cBN) as conventional superhard materials have found widespread industrial applications, but both have inherent limitations. Diamond is not suitable for high-speed cutting of ferrous materials due to its poor chemical inertness while cBN is only about half as hard as diamond. Because of their affinity in structural lattices and covalent bonding character, diamond and cBN could form alloys that can potentially fill the performance gap. However, the idea has never been demonstrated because samples obtained in previous studies were too small to be tested for their practical performance. In this talks, we report the synthesis and characterization of transparent bulk diamond-cBN alloy compacts whose diameters (3 mm) are sufficiently large for them to be processed into cutting tools. The testing results show that the diamond-cBN alloy has superior chemical inertness over polycrystalline diamond (PCD) and higher hardness than polycrystalline cBN (PcBN). High-speed cutting tests on hardened steel and granite suggest diamond-cBN alloy is indeed a universal cutting material.
Wednesday, August 10, 11:30AM, BPB 217
Hydrogenated graphene by reaction at high pressure and temperature
Functionalisation of graphene with hydrogen could lead to pathways to more advanced graphene chemistry, allows us to study carbon-based hydrogen storage and provides a method for opening a bandgap in the material. By applying temperature and pressure to graphene inside a resistive-heated diamond anvil cell, it is possible to initiate the reaction to synthesise partially-hydrogenated graphene – and different P-T conditions result in different extents of hydrogenation.
Wednesday, May 25, 11:30AM, BPB 217
Crystal Growth and Exploration of New Heavy Fermion Compounds
Eric D. Bauer
Los Alamos National Laboratory
In science, great breakthroughs in understanding are often made when a new experimental technique is developed and applied to solve important problems. For instance, Percy Bridgman’s development of high pressure techniques, which earned him the 1946 Nobel Prize, paved the way for groundbreaking discoveries in the mineralogy deep within the Earth and other planets, super-hard materials, chemical processes, and even the origins of life on the ocean floor. High pressure has also been instrumental in tuning the inherent small energy scales (~1-100 K) of strongly correlated electron materials. Breakthroughs in understanding also come from the growth and characterization of new materials. In this talk, I will present a brief overview of different techniques for growing crystals of heavy fermion materials, including sintering, molten metal flux, arc-melting, Czochralski and Bridgman techniques, and describe their advantages and disadvantages. I will describe several cases in which crystal growth has led to advances in understanding of the physics of heavy fermion materials, either by the serendipitous discovery of compounds such as the prototypical heavy fermion CeMIn5 (M=Co, Rh, Ir) compounds, or when ultra-high purity materials are necessary, such as to explore the “hidden order” state of URu2Si2.
Wednesday, April 27, 11:30AM, BPB 217
HIGH PRESSURE SCIENCE AT NASA JSC – TOUR OF THE INTERIORS OF TERRESTRIAL PLANETS, COLLABORATIVE AND STUDENT OPPORTUNITIES
Jacobs JETS, NASA JSC, Houston, Texas
Research conducted in high pressure experiments at NASA Johnson Space Center emphasizes the petrology and processes of planetary differentiation. Our interests are understanding the roles that oxygen fugacity plays in controlling fundamental properties of differentiated planetary bodies, such as metallic core size, mantle FeO content, and general metal-silicate equilibrium. In addition, our work seeks a clearer understanding of chemical phase equilibria in planetary precursors, how the equilibria change at higher temperatures and pressures, and how they apply to planetary accretion and core formation. Also, we evaluate models of terrestrial planet formation and differentiation, the importance of magma ocean formation and solidification in terrestrial planets and planetesimals, late accretion, and the origin and effects of water and other geochemically volatile elements.
A tour of the inner solar system, featuring interiors and differentiation of terrestrial planets from each of our experimental facilities will be presented. We are a diverse and growing research group, with numerous opportunities for collaboration and student involvement. We welcome visitors to both our experimental and analytical facilities – find out how we can help you achieve your research goals.
Wednesday, Mar. 30th, 11:30AM, BPB 217
Phase Transitions at Extreme Conditions
Dr. Jeffery H. Nguyen
Lawrence Livermore National Laboratory
Accurate determination of phase boundaries of materials at extreme pressure and temperature conditions is of great interest to the high-pressure community. Our research at the light gas gun at Livermore has been focused on accurate measurement of equations of state and phase transitions of metals at high pressure, both on and off-Hugoniot. In this presentation, we will highlight our results on the melting pressures of Fe, Mo, and Ta. From the measured longitudinal sound velocities, we were able to simplify previously known Fe and Mo phase diagrams and confirm existing Ta phase diagram. Implications from these results will be discussed. To achieve off-Hugoniot states, we developed Graded Density Impactors (GDI), which allow us to tailor our compression paths. By using these GDIs, we were able to study new phenomena such as liquid-solid transition and its kinetics. We will highlight experiments on freezing of molten tin, iron and water on compression.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Friday, April 1st, 3:45 PM, BPB217
Spin-phonon interaction in uranium dioxide
Idaho National Laboratory
Uranium dioxide (UO2) is a Mott-Hubbard insulator with well-localized 5f-electrons and its crystal structure is the face-centered-cubic fluorite. It experiences a first-order antiferromagnetic phase transition at 30.8 K to a non-collinear antiferromagnetic structure that remains a topic of debate. Despite extensive experimental and theoretical efforts the nature of the competing degrees of freedom and their couplings (such as spin-lattice coupling) are still unclear. In this talk I will present results of our extensive transport and thermodynamic investigations, on well-characterized and oriented single crystals of UO2, performed at low temperatures and high magnetic fields up to 100 T. We were able to elucidate some important questions such as the detailed nature of the low temperature multidomain 3k-AFM state and its importance for linear coupling between the system’s magnetic polarization and mechanical strain, and the reasons behind unusual lattice properties that severely hinder the ability of this important nuclear material to transport heat. I will discuss implications of these results.
Beyond thermodynamic stability: synthetic pathways to new materials with exceptional properties
Multiple allotropes and/or chemical compounds can be formed under various pressure / temperature conditions, and some of these could remain metastable under standard conditions for time scales as long as the age of the universe (in fact it is estimated that 50% of all known inorganic compounds are metastable ones!). But the number of known allotropes/compounds pales in comparison with the number of hypothetical ones with energetic feasibility. For any given thermodynamic state, thousands of energetically competitive structures are plausible, a subset of which will exhibit mechanical stability. Further subsets of these structures offer enticing physical properties that differ from those of thermodynamic ground states. Here we delineate thermodynamic and kinetic synthesis methods and discuss strategies and examples for accessing these states experimentally. In particular, we discuss successful experimental realization of new forms of silicon and carbon.
March 17, 3:45 PM, BPB Conference Room
Shock compression spectroscopy of molecular and nano- materials
The recent study of optical properties of molecular organic materials and nanomaterials under extreme condition of high pressure are presented. The capability of using organic dyes as an ultrafast emission probe for real time monitoring of nanosecond viscoelastic shock compression of condensed matter and utilizing quantum dots for fabricating stress sensitive nanocomposites are demonstrated. It is also presented further capability of using fluorescent probes for studying shock effects in microstructured media that allows us to both visualize structural changes, such as particle cracking and disintegration, and to create a spatial map of the inhomogeneous micropressure distribution using well-known concepts drawn from the field of fluorescence microscopy.
Mar 11, 3:45 PM, BPB Conference Room
Extreme thermodynamic conditions: novel stoichiometries, violations of textbook chemistry, and intriguing possibilities for the synthesis of new materials.
As evidenced by numerous experimental and theoretical studies, application of high pressure can dramatically modify the atomic arrangement and electronic structures of both elements and compounds. However, the great majority of research has been focused on the effect of pressure on compounds with constant stoichiometries (typically those stable under ambient conditions). Recent theoretical predictions, using advanced search algorithms, suggest that composition is another important variable in the search for stable compounds, i.e. that the more stable stoichiometry at elevated pressures is not a priory the same as that at ambient pressure. Indeed, thermodynamically stable compounds with novel compositions were theoretically predicted and experimentally verified even in relatively simple chemical systems including: Na-Cl, C-N, Li-H, Na-H, Cs-N, H-N, Na-He, Xe-Fe. These materials are stable due to the formation of novel chemical bonds that are absent, or even forbidden, at ambient conditions.
Tuning the composition of the system thus represents another important, but poorly explored approach to the synthesis of novel materials. By varying the stoichiometry one can design novel materials with enhanced properties (e.g. high energy density, hardness, superconductivity etc.), that are metastable at ambient conditions and synthesized at thermodynamic conditions less extreme than that those required for known stoichiometries. Moreover, current outstanding questions, “anomalies” and “paradoxes” in geo- and planetary science (e.g. the Xenon paradox) could be addressed based on the stability of surprising, stoichiometries that challenge our traditional “textbook” picture. In this talk, I will briefly present recent results and highlight the need of close synergy between experimental and theoretical efforts to understand the challenging and complex field of variable stoichiometry under pressure. Finally, possible new routes for the synthesis of novel materials will be discussed.
This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Security, LLC under Contract DE-AC52-07NA27344.
January 29, 3:30 PM BPB Conference Room
Ultrafast Shock Compression Experiments to Rapidly Test Extreme Condition Materials Predictions
Dr. Joseph M. Zaug
Physical Chemist and Group Leader – High Pressure Chemistry Group – Materials Science Division, Lawrence Livermore National Laboratory, Livermore, CA, 94550
In this talk, we will discuss recent results from ultrafast tabletop laser compression experiments on fluids, polymers, and high energy density organic molecules including single crystals. Previous work on ultrafast shocked metals will be summarized and serve as an introduction to our technical approach. Extreme material theories benefit from this research through a growing understanding of how ultrahigh strain rate (108 -1011 s-1) loading processes affect later-time high-strain rate (104 -106 s-1) phenomena occurring on macroscale dimensions.
Larger scale gun-based compression platforms nominally generate 106 s-1 maximum equilibrated strain rate loads; however, initial rising transient strain rates —not measured— may actually reach ultrahigh values. At present, the ultrafast shock community currently utilizes diagnostics that measure hydrodynamic flow and UV/VIS absorption; however, these methods tell us nothing directly about structure or chemical states. (We can consider perspectives on the viability of potential solutions to this long-standing challenge.) Nonetheless, when we’ve matched —on identical temporal and spatial scales— hydrodynamic data with commensurate molecular dynamics or crystal mechanics simulation results, more comprehensive pictures materialize that further illuminate the progression of early-time shock induced phenomena, such as high-strain rate induced elastic to plastic wave transitions preceding chemical initiation. Definitive knowledge gaps are also discovered.
We will conclude this presentation with an example of how one may use ultrafast compression-quench experiments to freeze metastable intermediate products. Shockwave compression states normally release to high-temperature thermodynamic states governed by the heat capacity of the starting material; however, by stopping (at an early-stage) shock induced chemical decomposition, i.e., bond breaking, one can trap or even consider synthesizing previously inaccessible transient species. For example, diamond formation from shocked TATB (1,3,5-triamino-2,4,6-trinitrobenzene) had been predicted for decades and was finally proved correct using this novel experimental approach.
Dr. Joseph (Joe) Zaug – Founding member (1997) and leader of the High Pressure Chemistry Group within the Materials Sciences Division at Lawrence Livermore National Laboratory. (Ph.D. in Physical Chemistry, University of Washington, Seattle, 1994; B.S. in Chemistry, Illinois Institute of Technology, 1988) He has twenty-five years of experience developing tools that quasi-statically and/or dynamically compress materials and engineering new approaches to characterize extreme condition material response using primarily laser-based systems. Numerous grand-challenge science issues have been met by these innovations resulting in high-profile publications in disciplines such as geophysics, high-pressure physics and chemistry including chemical synthesis, and materials science. Joe and his group actively collaborate with international and U.S. collaborators. His current research focus is on measuring equations of state and physical or chemical phase transitions of single crystals, polymers, and composite materials subjected to quasi-static and ultrahigh strain rate loads. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344
December 8, I:OO PM BPB Conference Room
Cation order-disorder in crystalline solids: case studies in orthopyroxene and magnetite
Effects of cation order-disorder in crystalline phases have received much attention because of their importance in solid state physics, material sciences, mineral physics and geochemistry. Cation order-disorder plays a key role in the crystal chemistry, energetics and physical properties of solids and may alter crystal symmetry and change material properties such as the electrical and thermal conductivity and elastic moduli. Understanding of the order-disorder process can provide us powerful tools for deciphering Planets’ history of evolution. I will present two examples from my own research experience for the seminar.
December 15, I:OO PM BPB Conference Room
Oliver Tschauner and Amber Turner
The Synthesis of Ringwoodite in Shock Compression Experiment of Olivine Crystals
Whereas, Ringwoodite is a rock-forming, high pressure silicate phase that occurs naturally within the Earth’s mantle and in shocked meteorites produced as the result of the transformation of olivine at high pressure during shock impact. However, it is not clear if crystal growth and transformation rates from static high pressure-high temperature experiments can be applied to dynamic stresses. In order to resolve whether or not crystal growth can be attributed to dynamic stresses, one must simulate the natural occurrences of Ringwoodite by creating a local shock-melt pocket as it occurs in nature. The overall objective of shocking olivine crystals is to investigate the kinetic barriers of Ringwoodite: the time of shock duration that must elapse in order for the formation of Ringwoodite to occur in shocked meteorites and how much overrun pressure is needed (at what temperature) to achieve the synthesis of Ringwoodite. For the synthesis of Ringwoodite to be achieved, I will expose olivine single crystal sample assemblies to shock pressures between 15 and 40 GPa at the shockwave laboratory of the Department of Geoscience. In order to observe where in the shock metamorphic process that Ringwoodite is synthesized, my research methods will rely on synchrotron micro X-ray diffraction of the thin sections of the newly shocked olivine sample. Synchotron data will exhibit the grain size of Ringwoodite, which I will then compare to naturally occurring Ringwoodite. Grain size will give insight as to the growth rate at which Ringwoodite is formed, correlating it with shock duration and making it possible to determine crystalline growth rates.
November 17, I:OO PM BPB Conference Room
Shining Light on Matter
This talk will focus on the current and future capabilities of the Salamat Lab. The main topics covered will be on how to generate and measure high temperatures within the confinements of the diamond anvil cell (DAC), with an over view on different melting criteria. Optical spectroscopy of solid state systems will be discussed with special attention on the possibility of carrying out Raman spectroscopy on metals under high pressure.
November 10, I:OO PM BPB Conference Room
PREDICTIVE MODELING OF TERRESTRIAL RADIATION EXPOSURE FOR GEOLOGIC MATERIALS
Aerial gamma ray surveys are an important tool for national security, scientific, and industrial interests in determining locations of both anthropogenic and natural sources of radioactivity. There is a relationship between radioactivity and geology and in the past this relationship has been used to predict geology from an aerial survey (Moxham 1963; Pitkin, Bates et al. 1964). The purpose of this project is to develop a method to predict the radiologic exposure rate of the geologic materials in an area by creating a model using geologic data, images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), geochemical data, and previously existing aerial surveys from the National Uranium Resource Evaluation (NURE) Survey. Using these data, geospatial areas that are homogenous in terms of K, U and Th are defined and the gamma ray exposure rate is predicted. The prediction is compared to data collected via detailed aerial survey by our partner National Security Technologies, LLC (NSTec), allowing for the refinement of the technique. Models have been developed in two study areas in Southern Nevada that include the alluvium on the western shore of Lake Mohave, and Government Wash north of Lake Mead; both of these areas are arid with little soil moisture and vegetation. In general, we determined that by using geologic units to define the geospatial areas of exposed bedrock and ASTER visualizations to break up and define the geospatial areas of alluvium and colluvium, regions of homogenous geochemistry can be defined allowing for the exposure rate to be predicted for each region. This work was done by National Security Technologies, LLC, under Contract No. DE‐AC52‐06NA25946 with the U.S. Department of Energy and supported by the Site‐Directed Research and Development Program.
References Moxham, R. (1963). “Natural Radioactivity In Washington County, Maryland.” Geophysics 28: 262‐272.
Pitkin, J., R. Bates, et al. (1964). “Aeroradioactivity surveys and geologic mapping (Nuclear facility background gamma radiation measured by aerial radiological measurement).” The Natural Radiation Environment: 723‐736.
Ph.D. Defense – Friday, Nov. 13 at 10:30 AM in BPB 248
High Pressure X-Ray Absorption Spectroscopy Studies of Heavy-Fermion Cerium and Uranium Compounds
Investigations into f- electron heavy-fermion materials have revealed a wide range of novel behavior. Hydrostatic pressure is a valuable “clean” non-thermal parameter that can be used to systematically study them by tuning their ground state properties. The rare earth compound CeCu2Ge2 shows an unusual two-domed region of unconventional superconductivity under pressure, similar to its isostructural counterpart CeCu2Si2. While the lower pressure dome at about 10 GPa is caused by a magnetic quantum critical point, the higher one at about 16 GPa is less well understood. Previous structural measurements have indicated that it may be caused by critical valence fluctuations, so in this study the valence of CeCu2Ge2 is directly measured using X-ray Absorption Near Edge Spectroscopy (XANES) under pressure in a diamond anvil cell up to 20 GPa. An expected valence discontinuity is not seen, but comparisons to CeCu2Si2 show interesting similarities. Uranium’s 5f electrons are intermediate between localized and delocalized. Studying the degree of localization is vital to completely understanding properties of actinides. Using XANES and partial Florescence Yield (PFY) in a diamond anvil cell to tune the distance between uranium atoms, I have measured the energy shift in the white line of UCu2Si2, U3Ni5Al19, and UCd11 with pressure. A positive shift in energy indicated a delocalization of 5f electrons, a change in 5f configurations, or a combination of both.
November 3, I:OO PM BPB Conference Room
Hall Effect Measurements
Hall effect measurements are the best method to study the charge carrier behaviors in materials and have been widely used in physics and material science. Taking Hall effect measurements in a diamond anvil cell is still challenging. This talk will go over the basics of the Hall effect and quantum Hall effect. Techniques that have been used at high pressures inside a DAC will be discussed as well as possible applications to study the quantum anomalous hall effect in magnetic topological insulators under pressure.
Oct 27, 2015 BPB Conference Room, 1:00 PM
Professor, Dept. Physics & Astronomy
Deputy Director of HiPSEC
Plutonium: A Curious Element
Plutonium (atomic number 94) does not occur naturally but is vitally important as a fissile element. However, much is still not known about the physical behavior of Pu. Understanding how Pu ages as it continually undergoes self-damage is one of the main goals of the Stockpile Stewardship Program under which HiPSEC is supported.
From a pure physics point of view, Pu displays very interesting properties. I will review the electronic, magnetic, and structural properties of Pu and Pu compounds and discuss how studies on other d- and f-electron materials are relevant to our understanding of Pu.
Oct 20, 2015 BPB Conference Room, 1:00 PM
Nudged Elastic Band Method for finding minimum energy paths
In Condensed Matter Physics and Chemistry often one would like to know the lowest energy path from one stable structure state to another. The problem is a minimum energy path (MEP) is described by passing through a saddle point, where the maximum potential energy along the MEP gives the activation energy. There are many different types of methods to find the MEP and saddle points. I will present several methods for finding the MEP, including nudged elastic band method, and give efficiency explanations for computational calculations.
Oct 6, 2015 BPB Conference Room, 1:00 PM
Developing New Detectors for Neutron Measurements
Typically, most types of nuclear measurements to date have utilized photomultiplier tubes (PMT’s) for scintillation measurements. The downfall of PMT’s is that they are very large and require a very high voltage ( 1000+ V) to operate. These requirements have made it difficult to create deployable detectors for neutron measurements in the field. Utilizing silicon tied together in an array, voltage signals on the order of PMT’s can be generated. These arrays, called Silicon Photomultipliers (SiPM’s), show a large promise for replacing PMT’s due to there very small size, as well as the fact that operate on a very low voltage bias (<30V). One of the major problems with SiPM’s is that there are intrinsic electronic issues that skew any timing information from scintillation events, making pulse shape discrimination measurements very difficult. To help correct this downfall, a circuit had to be developed to help improve the performance of a SiPM based detector. Recent work on this circuit shows high promise for future development and deployment of SiPM based detectors.
Nolan Regis and Pamela Burnley
August 25, I:OO PM BPB Conference Room
Phase Equilibria of Quartz Under Stress
Analyze the response of polycrystalline quartz to differential stress using two-dimensional (2D) plane-strain finite element models (FEMs) and high pressure and temperature deformation experiments. To quantify effects of competing parameters (boundary conditions, stress state and strain) I used a variety of sample shapes in 2D plane-strain FEMs of a hypothetical elastic-plastic polycrystalline material. Deformation experiments will be conducted with a modified piston cylinder high pressure and temperature apparatus (Griggs Rig) to reproduce the models. With compression, cylinders modified with an “hourglass” shape in the FEMs show an accumulation of Von Mises stress at the midpoints of the arcs. Deformation experiments have not been performed, but are expected to behave similarly and flow laterally to accommodate the high stress at the center of the sample. Understanding the stress conditions that form diagnostic ultrahigh-pressure minerals such as coesite (polymorph of quartz) in small-scale deformation experiments can impact how we estimate the burial depth of tectonic units. Quantifying the phase equilibria of quartz under stress will allow us to improve the accuracy of pressure-depth estimations of metamorphosed rocks.
August 18, I:OO PM BPB Conference Room
Synthesis and Characterization of Bi4O4S3
The recent discovery of the superconducting phase in Bi4O4S3 could potentially revive the
search for superconductivity in a wide range of layered sulfides. These materials are characterized by large, layered unit cells which mimic those of the high-Tc CuO2 cuprates and FeAs pnictides – whose superconducting mechanisms are still not well understood. Thus, the scientific interest in layered sulfide superconductors is stimulated by the expectation that the study of such materials could provide valuable insight into the superconducting mechanisms at work within structurally similar unconventional superconductors. My talk will report on the successful synthesis of the layered sulfide superconductor, Bi4O4S3 (Tc = 4.5K), and will include a discussion of the various experimental techniques utilized to characterize superconducting samples under both ambient and extreme pressure conditions.
July 21, I:OO PM BPB Conference Room
Neutron scattering for non ambient experiments
X-Ray diffraction is the primary diagnostic used in high pressure experiments, particularly in diamond anvil cells. Optical spectroscopy and neutron scattering are viable techniques for materials investigation at non ambient conditions. This talk will cover the many aspects of neutron scattering experiments including fundamental neutron properties and interaction mechanism, neutron experiments, sources and facilities.
July 7, I:OO PM BPB Conference Room
Infrared spectroscopy is a popular and informative analytical method used in many fields of science, particularly chemistry. A molecule subjected to infrared radiation will absorb certain frequencies based on the types of bonds present and vibrations of the bonds. The theory, requirements, and advantages of infrared spectroscopy will be discussed, especially in regards to the application of this technique in high pressure physics. Examples of different laboratory set ups will be presented, including those at the Canadian Light Source, where Dr. Pravica’s group has conducted some of the first diamond anvil cell experiments at the CLS mid-IR and far-IR beamlines.
June 30, I:OO PM BPB Conference Room
Large-volume press (LVP) is a complementary capability to the diamond anvil cell (DAC). The LVP uses larges presses to compress large volumes compared to the DAC (10^3 to 10^6 times more). Although the LVP is limited in its PT range, it offers more uniform and reliable PT conditions than a DAC. The LVP also has more hydrostatic conditions. The stability of the LVP makes it ideal for accurate determination of equation of state and bulk physical properties. In this lecture various LVPs and there mechanics are described.
June 2, I:OO PM BPB Conference Room
Radiation Detection and Equipment
Radiation detection is used in many fields of scientific study. There are a number of methods to detect radiation. Understanding radiation sources and interaction mechanisms while using the proper detection equipment is vital to obtaining the results you are looking for. This talk discusses types of radiation, interaction mechanisms, radiation detectors and their operation, advantages and disadvantages of different types of detectors, and their best case usage scenario. In addition, Monte Carlo simulations of radioactive emissions can be built with the properties of the appropriate detector built in to test real world scenarios.
May 26, I:OO PM BPB Conference Room
Battery properties are a growing trend in today’s research fields. The search for increasingly better cathode, anode and electrolyte materials is an ongoing process that can have a wide variety of positive impacts on numerous industries. Within this search are a great many possibilities of which will greatly increase our current battery capacities and functionality. One of the greatest advances in battery technology could come from what is known as the Lithium Air battery. Within this talk I plan to explore the current research taking place in order to make this theoretical battery a reality along with the technical possibilities it could bring to our every day lives very soon.
May 19, I:OO PM BPB Conference Room
Topological insulators are materials that have a bulk band gap like an ordinary insulator but have protected conducting states on their edge or surface. Recent experiments on Bi1−xSbx, Bi2Se3, Bi2Te3, and Sb2Te3 established these materials as 3D topological insulators. Bi2Te3 has been shown to superconduct under pressure coinciding with a structural transition from a rhombohedral to a monoclinic structure. There is much interest in whether the surface states in topological insulators can be tuned to give rise to topological superconductivity. Presented here are basic concepts of topological insulators and recent high pressure studies of Bi2Te3 and Mn doped Bi2Te3.
May 5, I:OO PM BPB Conference Room
Phonons are a key carriers for heat transport. Important physical properties like thermal conductivity, heat capacity, and group velocity can be calculated from phonons. Phonons are also used for determining structure stability. This talk will be able the phonon transport theory. This includes different phonon interactions, the meaning of harmonic and anharmonic phonons, How to get the important thermodynamic properties from phonon frequencies. Furthermore, I will talk about software packages I developed in C++ and others developed and a how they calculate phonons.
Ph.D. Dissertation Defense
May 1, 10-30 AM to 12.30 PM VENUE: TBE A-120
STRUCTURE AND OPTICAL PROPERTIES OF TRANSITION METAL DICHALCOGENIDES (TMDs) – MX2 (M = MO, W & X = S, Se) UNDER HIGH PRESSURE AND HIGH TEMPERATURE CONDITIONS
Layered structured materials such as transition metal dichalcogenides (TMDs) have gained immense interest in recent times due to their exceptional structural, electrical and optical properties. Recent studies show semiconducting TMDs such as MX2 (M= Mo, W & X = S, Se) could be used as potential shock absorbing material, which has resulted in extensive studies on structural stability of these materials under the influence of high pressure. Understanding the structural stability of transition metal dichalcogenides (TMDs) such as MoS2, MoSe2, WS2, and WSe2 under high pressure has been very challenging due to contradicting observations and interpretations reported in the past. Hence, the main objective of this work is to study the crystal structure and optical properties of bulk MX2 at high hydrostatic pressures up to 51 GPa using a diamond anvil cell with synchrotron radiation in addition to high pressure Raman spectroscopic and high temperature X-ray diffraction (XRD) experiments. Crystal structures of MX2 materials are observed to be stable up to 500 oC with nonlinear thermal coefficients of expansion. Results of high pressure experiments show a pressure induced isostructural hexagonal distortion to a 2Ha-hexagonal P63/mmc phase in MoS2 around 26 GPa as predicted by theoretical calculations reported earlier. No pressure induced phase transformation is observed in other MX2 (MoSe2, WS2, WSe2) compounds. A semi empirical model based on the energy of interaction of bond electrons is proposed to explain the observed inconsistency between MoS2 and other TMDs studied. Using this model, it is shown that except MoS2, no other MX2 within the scope of this study undergoes pressure induced phase transition in the pressure range 0 – 50 GPa. High pressure Raman results show continuous red shifts in dominant vibrational modes with increase in pressure in MX2. Additionally, emergence of a new peak, namely ‘d – band’ associated with 2Ha structure in MoS2 supports the observation of a isostructural phase transition in high pressure X-ray diffraction experiments. In addition to the studies on bulk MoS2 material, thin film (approximately 100 nm thicknesses) is successfully fabricated via DC magnetron sputtering system and sulfurization technique.
April 28, 2015 1:00 PM BPB Conference Room
Single Crystal X-Ray Diffraction Study of GaP with Diamond Anvil Cell
I will present my research on the low and high pressure phases of gallium phosphide, including experimental refinement of the ambient phase parameters and bulk modulus obtained through single crystal X-ray micro diffraction techniques. This study advances the literature in our understanding of the GaP structure because of the experimental techniques of single crystal diffraction, heating methods, and use of neon – a more hydrostatic medium for applying isotropic pressure in the sample chamber than used in previous experiments. The literature brings an interesting and inconclusive understanding of the high pressure phase of GaP, including predictions and results of tetragonal, cubic, and orthorhombic unit cell possibilities. I will expound on the literary history of GaP and discuss how our research will provide further clarity and insight as to the high pressure phase.
April 21, 2015 1:00 PM BPB Conference Room
Synthesis and High Pressure Investigation of Superconducting Materials
In this talk, I will present an overview of the high pressure techniques for studying the transport properties (resistivity) and structure of superconducting materials. Specifically, the results obtained on Nb-based materials and MgB2 will be discussed. Further, results on synthesis and preliminary characterization of Bi-2212 superconductor using a Vertical Bridgman furnace will be presented.
March 24, 2015
M.S. student Richard Rowland
Phase equilibria of bastnaesite-(La)
Bastnaesite (Ce,La,Y)CO3(F,OH) is a Rare Earth Element (REE) ore mineral. REEs are more common in the Earth’s crust than precious metals like gold or platinum, but are not commonly concentrated in economically viable ore deposits. For over a decade, China has been the world’s leading supplier of REEs. Recent export restrictions from China have necessitated the search for new deposits. Determining the temperature and pressure stability field for bastnaesite will help in understanding the processes that form REE ore deposits and thereby assist in locating new deposits (Haxel, et al. 2002).
This study focuses on the lanthanum-fluoride variant of bastnaesite (LaCO3F) since it can be reliably synthesized in the laboratory. Also, some testing has been done with natural bastnaesite ore from Mountain Pass to ensure that experimental results with synthetic bastnaesite are applicable to the real world. Previous experimental work determined that in both open and closed systems at atmospheric pressures bastnaesite decomposes to Lanthanum Oxyfluoride (LaOF) at 325°C. At 100 MPa, bastnaesite was found to be unstable at temperatures exceeding 860°C (Hsu, 1992).
Using a Griggs-type modified piston cylinder apparatus, several samples of synthetic and natural bastnaesite were pressurized between 250 MPa and 1.2 GPa and subjected to temperatures between 700°C and 1050°C for at least five hours. X-ray powder diffraction (XRD) was used to analyze the samples and determine the mineral phases present after each experiment. It has been determined that bastnaesite is stable at 250 MPa up to approximately 800°C and at 1.0 GPa up to approximately 900°C.
March 17, 2015
Ph. D. Student Emily Siska
“Novel Radionuclide Wasteforms Prepared Under Pressure”
Currently, the most widely used waste form for nuclear waste is borosilicate glass. Although glass and ceramic waste forms have proven to be durable and sufficient at immobilizing many radionuclides; they are not ideal for certain radionuclides including I2, Kr, Tc and actinides. These nuclear waste products have long half-lives and have particularly harmful health and environmental effects. There is a need to design new waste forms that can immobilize these problematic radionuclides and reliably store them for thousands – and in some cases millions of years. Zeolites are a family of either naturally occurring or synthetic aluminosilicate minerals composed of Earth-abundant, inexpensive, low toxicity elements. Sodalite is a type of zeolite that is comprised of cages with windows smaller than the diameters of the intended guests. It is has been show that under certain conditions the windows can accommodate diffusion of larger guest atoms/molecules. Lattice distortions and vibrations brought on by pressure and temperature can make the structure flexible enough to allow for the diffusion of small molecules/ions. Compression of the rhombohedral form of silica-sodalite was performed in different media in hopes of learning the behavior and capabilities of the structure and how to possibly improve it for waste immobilization. Also, using General Utility Lattice Program (GULP) we predict pressure dependent changes to the structures.
March 3, 2015
Ph. D. Student Jason Baker
“Theory and Measurement Techniques for Thermal and Electrical Properties of Thermoelectric Compounds”
Thermoelectric materials see a wide range of applications including commercial portable refrigeration, spot heating/cooling of electronic circuitry, waste heat conversion, and thermoelectric generators both commercially and industrially. Understanding the basic thermal and electrical properties such as electrical resistance, thermopower, and thermal conductivity is paramount to discovering better materials. The underlying theory of these properties and measurement techniques will be discussed.
February 24, 2015
Ph.D. Student Daniel Antonio
“X-ray Absorption Spectroscopy at High Pressure”
X-ray absorption spectroscopy can be used to study the local structural and electronic properties of a specific atom in a compound. An intense monochromatic X-ray source is scanned across the absorption energy of a core electron, and the either the transmitted beam or the resulting fluorescence is measured. The theory and advantages of different techniques will be discussed, as well as the challenges of using them in a diamond anvil cell.
February 17, 2015
Dr. Jinlong Zhu
“Local structure study of perovskite materials by pair distribution function as functions of temperature and pressure“
Local structures are often distorted from long-range average crystal structure in perovskite materials. Characterization of such structural distortion is critical to understanding their electronic, magnetic and dielectronic properties. Pair distribution function (PDF) method has been proved to be an effective tool to determine differences between the local and the average crystal structures by using Fourier transform of the coherent and incoherent scattering. It is capable of revealing atomic correlations from several Angstroms (local structure) to several hundred Angstroms (averaged structure). Typical applications include atomic-scale structural resolutions of nanoparticles, amorphous phases, and disordered crystalline materials. In this talk, examples including wax-infiltrated carbon nanotube sponges, and two perovskite compounds of LaMnO3 and BiNi1/2Ti1/2O3 are introduced to demonstrate the capability of PDF.
Daniel Sneed, Dec 9, 2014
For the past few years, Dr. Michael Pravica’s group has been working to develop a new technique to form molecular gases in situ within a diamond anvil cell. By utilizing the highly ionizing and penetrating characteristics of hard x-rays, we have been able to break down relatively inert compounds, allowing the ionized atoms to react and form stable molecular gases. Over the past two years we have been able to successfully form multiple molecular gases, the most recent of which being molecular fluorine. Recent theoretical work postulates the existence of cesium in high oxidation states when bonding with fluorine, behaving as a P-block element like Xenon at pressures above 30 GPa. It is our goal to physically synthesize these compounds and verify that, given the right conditions, bonding doesn’t only happen with valence electrons, but the inner P-shell electrons as well. Verification of this behavior could potentially open the door to a whole new understanding of chemical bonding.
Melanie White, Dec 2, 2014
Research in Dr. Michael Pravica’s group for the last few years has been focused primarily on developing a technique for the use of x-ray radiation to initiate chemical reactions within a Diamond Anvil Cell. One of the successes of this technique has been in producing molecular gasses like H2, O2, and F2 in situ, which are otherwise very difficult to load in a DAC. In particular, the production of F2 is very exciting. This presentation will include a brief discussion of creating F2 in a DAC, with the primary focus on current research efforts to create new CsFn compounds.