Papers by Leonid Burakovsky
Frontiers in Nuclear Engineering, Jan 2, 2024
As UO 2 is easily oxidized during the nuclear fuel cycle it is important to have a detailed under... more As UO 2 is easily oxidized during the nuclear fuel cycle it is important to have a detailed understanding of the structures and properties of the oxidation products. Experimental work over the years has revealed many stable uranium oxides including UO 2 , U 4 O 9 (UO 2.25 ), U 3 O 7 (UO 2.33 ), U 2 O 5 (UO 2.5 ), U 3 O 8 (UO 2.67 ), and UO 3 , all with a number of different polymorphs. These oxides are broadly split into two categories, fluorite-based structures with stoichiometries in the range of UO 2 to UO 2.5 and less dense layered-type structures with stoichiometries in the range of UO 2.5 to UO 3 . While UO 2 is well characterized, both experimentally and computationally, there is a paucity of data concerning higher stoichiometry oxides in the literature. In this work we determine the ambient melting points of all the six stoichiometric uranium oxides listed above and compare them to the available experimental and/or theoretical data. We demonstrate that a family of the six ambient melting points map out a solid-liquid transition boundary consistent with the high-temperature portion of the phase diagram of uranium-oxygen system suggested by Babelot et al.
Applied sciences, May 22, 2023
Mixed oxides of uranium and plutonium (MOX) are currently considered as a reference fuel for the ... more Mixed oxides of uranium and plutonium (MOX) are currently considered as a reference fuel for the new generation of fast breeder reactors such as ASTRID. The key factor determining the performance and safety of a fuel such as MOX is its operational limits in the application environment which are closely related to the material's structure and thermodynamic stability. They are in turn closely related to the ambient (zero pressure) melting point (T m ); thus, T m is an important engineering parameter. Furthermore, PuO 2 and UO 2 are two endpoints of the phase diagram of MOX; therefore, their ambient T m s are fundamental reference points. However, the current knowledge of the T m of MOX is limited and controversial as several studies available in the literature do not converge on the unique behavior of T m as a function of x. Specifically, some studies produced T m as a monotonically decreasing function of x such that, with T m of UO 2 (x = 0) of 3150 K, T m of PuO 2 (x = 1) is ∼2650 K, while other studies resulted in T m having a local minimum at 0.5 < x < 1 such that T m of PuO 2 is ∼3000 K, so that the difference between the two values of T m is as high as 350 K. In this study, using the ab initio Z method implemented with the Vienna Ab Initio Simulation Package (VASP), we carry out a suite of quantum molecular dynamics simulations to obtain the ambient T m of MOX at several values of x, 0 < x < 1, including the two end points (x = 0, x = 1). Our results agree with the behavior of T m of MOX as a function of x having a local minimum at x = 0.7 and T m of PuO 2 of 3050 K. Our study suggests potential ambient density-melting point systematics of MOX which may be useful in subsequent research on MOX such as its thermoelasticity modeling.
Matter and Radiation at Extremes
Although they are polymorphic (multiphase) materials, both copper and silver are reliable Hugonio... more Although they are polymorphic (multiphase) materials, both copper and silver are reliable Hugoniot standards, and thus it is necessary to establish an accurate analytic model of their principal Hugoniots. Here we present analytic forms of their principal Hugoniots, as well as those of iridium and platinum, two “pusher” standards for shock-ramp experiments, over a wide range of pressures. They are based on our new analytic model of the principal Hugoniot [Burakovsky et al., J. Appl. Phys. 132, 215109 (2022)]. Comparison of the four Hugoniots with experimental and independent theoretical data (such data exist to very high pressures for both copper and silver) demonstrates excellent agreement. Hence, the new model for copper and silver can be considered as providing the corresponding Hugoniot standards over a wide pressure range. We also suggest an approach for calculating the Grüneisen parameter along the Hugoniot and apply it to copper as a prototype, and our results appear to be in ...
Acta Materialia, Jun 1, 2022
Metals
Under dynamic loading conditions and the associated extreme conditions many metals will undergo p... more Under dynamic loading conditions and the associated extreme conditions many metals will undergo phase transformations. The change in crystal structure associated with solid–solid phase transformations can significantly alter the subsequent mechanical response of the material. For the interpretation of experiments involving dynamic loading it is beneficial to have a modeling framework that captures key features of the material response while remaining relatively simple. We introduce a candidate framework and apply it to the metal tin to highlight a range of behaviors that are captured by the model. We also discuss potential extensions to capture additional behaviors that could be important for certain materials and loading scenarios. The model is useful for analysis of results from dynamic experiments and offers a point of departure for more complex model formulations.
The high-pressure and high-temperature melting curve of chromium has been investigated both exper... more The high-pressure and high-temperature melting curve of chromium has been investigated both experimentally (in situ), using a laser-heated diamond-anvil cell technique coupled with synchrotron powder X-ray diffraction, and theoretically, using ab initio density-functional theory simulations. In the pressure–temperature range covered experimentally (up to 90 GPa and 4500 K, respectively) only the solid body-centred-cubic and liquid phases of chromium have been observed. Experiments and computer calculations give melting curves in agreement with each other, that can be described by a Simon–Glatzel equation Tm(P) = 2136K(1+P/25.9) 0.41. In addition, a quasi-hydrostatic equation of state at ambient temperature has been experimentally characterized up to 131 GPa and compared with the present simulations. Both methods give very similar third-order Birch-Murnaghan equations of state with a bulk modulus of 182-185 GPa and its pressure derivative of 4.74-5.15. According to the present calcul...
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Mar 13, 2020
Bulletin of the American Physical Society, Jul 9, 2013
phase diagram studies. It combines direct Z method for the calculation of melting curves, and inv... more phase diagram studies. It combines direct Z method for the calculation of melting curves, and inverse Z method for the calculation of solid-solid phase boundaries. Relative solid phase stability is studied by comparing melting curves of different solid phases to determine which one is the highest, and thus which of the corresponding solid phases is the most stable. is accomplished using direct Z method. Subsequently, solid-solid phase boundaries can be determined by freezing liquid into the most stable solid phases on both sides of the phase boundary. Inverse Z method represents the implementation of this approach in terms of ab initiomolecular dynamics using VASP package. We will discuss the application of Z methodology to the study of the phase diagrams of tantalum and platinum, and compare our results to the most recent experimental data.
Journal of Applied Physics, Jul 28, 2020
Recent progress in the development of dynamic strength experimental platforms is allowing for unp... more Recent progress in the development of dynamic strength experimental platforms is allowing for unprecedented insight into the assumptions used to construct constitutive models operating in extreme conditions. In this work, we make a quantitative assessment of how tantalum strength scales with its shear modulus to pressures of hundreds of gigapascals through a cross-platform examination of three dynamic strength experiments. Specifically, we make use of Split-Hopkinson pressure bar and Richtmyer-Meshkov instability experiments to assess the low-pressure strain and strain rate dependence. Concurrent examination of magnetically driven ramp-release experiments up to pressures of 350 GPa allows us to examine the pressure dependence. Using a modern description of the shear modulus, validated against both ab initio theory and experimental measurements, we then assess how the experimentally measured pressure dependence scales with shear modulus. We find that the common assumption of scaling strength linearly with the shear modulus is too soft at high pressures and offer discussion as to how descriptions of slip mediated plasticity could result in an alternative scaling that is consistent with the data.
Communications materials, Aug 13, 2020
Compared to other body-centered cubic (bcc) transition metals, Nb has been the subject of fewer c... more Compared to other body-centered cubic (bcc) transition metals, Nb has been the subject of fewer compression studies and there are still aspects of its phase diagram which are unclear. Here, we report a combined theoretical and experimental study of Nb under high pressure and temperature. We present the results of static laser-heated diamond anvil cell experiments up to 120 GPa using synchrotron-based fast x-ray diffraction combined with ab initio quantum molecular dynamics simulations. The melting curve of Nb is determined and evidence for a solid-solid phase transformation in Nb with increasing temperature is found. The high-temperature phase of Nb is orthorhombic Pnma. The bcc-Pnma transition is clearly seen in the experimental data on the Nb principal Hugoniot. The bcc-Pnma coexistence observed in our experiments is explained. Agreement between the measured and calculated melting curves is very good except at 40-60 GPa where three experimental points lie below the theoretical melting curve by 250 K (or 7%); a possible explanation is given.
Applied Sciences
We present the analytic forms of the principal Hugoniots of actinium (Ac) and the lanthanide prom... more We present the analytic forms of the principal Hugoniots of actinium (Ac) and the lanthanide promethium (Pm), which have both never been measured or calculated before, as well as those of terbium (Tb), thulium (Tm), and lutetium (Lu), the three least studied of the remaining lanthanides. They are based on our new analytic model of principal Hugoniot. A comparison of the five Hugoniots to our own independent theoretical calculations demonstrates very good agreement in every case, but each of the Hugoniots of Tb, Tm, and Ac from the TEFIS database, which ours are also compared to, appear to violate Johnson’s theoretical constraint 4<ηmax<7 for the maximum compression ratio ηmax, which corresponds to the Hugoniot turnaround point. Possible reason for this behavior of the TEFIS Hugoniots is briefly discussed.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Jul 13, 2011
Journal of Physics: Condensed Matter, Jun 25, 2018
The phase diagram of zinc (Zn) has been explored up to 140 GPa and 6000 K, by combining optical o... more The phase diagram of zinc (Zn) has been explored up to 140 GPa and 6000 K, by combining optical observations, x-ray diffraction, and ab initio calculations. In the pressure range covered by this study, Zn is found to retain a hexagonal close-packed (hcp) crystal symmetry up to the melting temperature. The known decrease of the axial ratio (c/a) of the hcp phase of Zn under compression is observed in x-ray diffraction experiments from 300 K up to the melting temperature. The pressure at which c/a reaches √ 3 (≈10 GPa) is slightly affected by temperature. When this axial ratio is reached, we observed that single crystals of Zn, formed at high temperature, break into multiple poly-crystals. In addition, a noticeable change in the pressure dependence of c/a takes place at the same pressure. Both phenomena could be caused by an isomorphic second-order phase transition induced by pressure in Zn. The reported melt curve extends previous results from 24 to 135 GPa. The pressure dependence obtained for the melting temperature is accurately described up to 135 GPa by using a Simon-Glatzel equation: T m = 690 K(1 + P 10.5 GPa) 0.76 , where P is the pressure in GPa. The determined melt curve agrees with previous low-pressure studies and with shock-wave experiments, with a melting temperature of 5060(30) K at 135 GPa. Finally, a thermal equation of state is reported, which at room-temperature agrees with the literature.
Nuclear Physics, 1998
The new SU(3) nonet mass formula 2M 2 (ss)+3M 2 (nn, I = 1) = 4M 2 (sn)+ M 2 (nn, I = 0) (n = u, ... more The new SU(3) nonet mass formula 2M 2 (ss)+3M 2 (nn, I = 1) = 4M 2 (sn)+ M 2 (nn, I = 0) (n = u, d), obtained in our previous paper by using Regge phenomenology, is rederived for the pseudoscalar and scalar mesons in the Nambu-Jona-Lasinio model with instanton-induced interaction and applied to the problem of the correct qq assignment for the scalar meson nonet. The results strongly favor the masses of the scalar isoscalar mostly octet and mostly singlet states in the vicinity of 1.45 GeV and 1.1 GeV, respectively.
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Papers by Leonid Burakovsky