scholarly journals Ab Initio Study of the Effect of Mono-Vacancies on the Metastability of Ga-Stabilized δ-Pu

2020 ◽  
Vol 10 (21) ◽  
pp. 7628
Author(s):  
Sarah C. Hernandez ◽  
Franz J. Freibert
Keyword(s):  
First Principles ◽  
Room Temperature ◽  
Experimental Studies ◽  
Tetragonal Distortion ◽  
Ab Initio Study ◽  
Α Phase ◽  
Fcc Lattice ◽  
Δ Phase ◽  
A Site ◽  
Electronic Behavior

Most experimental studies on metallic Pu are on the room temperature monoclinic α-phase or the fcc Ga stabilized δ-phase. Stabilized δ-phase Pu-Ga alloys are metastable and exhibit a martensitic phase transformation to α’-phase at low temperatures, or applied shear, with concentrations lower than three atomic percent Ga. By using first principles, we explore the metastability of δ-phase by investigating the structural and electronic behavior induced by Ga alloying and by a mono-vacancy point defect. We find that a site substitutional Ga induces a tetragonal distortion in the lattice affected by hybridization of Ga 4p and Pu 6d states. With the addition of a mono-vacancy, a monoclinic or tetragonal distortion forms locally (dependent on its distance from Ga), and decoupling of the Pu 5f and 6d states and broadening of the 6d states occurs. This response enables hybridization of Pu 6d with the Ga 4p states affecting the mono-vacancy formation energy. Thus, stabilization of the fcc lattice correlates with hybridization of Pu 6d states with Ga 4p states, and this becomes more evident in the presence of a mono-vacancy.

scholarly journals Experimental Studies on Frozen Soil

2021 ◽  
Author(s):  
Kshitij Gaur ◽  
Anil Kumar Sahu
Keyword(s):  
Room Temperature ◽  
Void Ratio ◽  
Experimental Studies ◽  
Soil Surface ◽  
Negative Temperature ◽  
Research Data ◽  
Frozen Soil ◽  
Soil Parameters ◽  
Frozen Soils ◽  
A Site

Abstract Various studies have been carried out for soils at normal room temperature but the studies on frozen soils are meagre. For every construction, soil investigation is the most important and the primary step for a site. For constructions at normal room temperature, there is plenty of experimentation and research data on soil is available. But lack of research data for colder regions, where the ambient temperature is below zero degrees Celsius for most of the time. It is therefore the need to study soil under the iced condition to get a better idea about the behaviour of frozen soils. There is little research on the construction and mechanical behaviour of frozen soil but no study on the very basic parameters like void ratio, bulk density, porosity, and the degree of freezing and how these parameters change as the soil temperature changes from normal room temperature to negative values. The main emphasis is on the study and experimentation of frozen soil and the formulation of different relationships between individual soil parameters at various temperatures. The methodology used is to model the soil surface (open grounds in colder regions) by taking sand as the soil after sieving. The model samples are taken into beakers with different bulk densities to replicate real site conditions in the freezer. Then by calculating factors like density, porosity, void ratio, etc at negative temperature (-5, -10, -15, -20 degree Celsius) and forming a relationship with the same parameters as that on room temperature. The experimental data obtained is used in “Eureqa software” that will utilize the input so provided and will find mathematical relations that exist in the soil parameters.

“Burst-like” Characteristics of the δ/α′ Phase Transformation in Pu-Ga Alloys

2003 ◽  
Vol 802 ◽  
Author(s):  
Kerri J.M. Blobaum ◽  
Christopher R. Krenn ◽  
Jeffery J. Haslam ◽  
Mark A. Wall ◽  
Adam J. Schwartz
Keyword(s):  
Phase Transformation ◽  
Room Temperature ◽  
Large Temperature ◽  
Temperature Hysteresis ◽  
Scanning Calorimetry ◽  
Α Phase ◽  
Δ Phase ◽  
Annealing Cycle ◽  
Heat Of Transformation ◽  
Start Temperature

ABSTRACTThe δ to α′ phase transformation in Pu-Ga alloys is intriguing for both scientific and technological reasons. On cooling, the ductile fcc δ-phase transforms martensitically to the brittle monoclinic α′-phase at approximately −120°C (depending on composition). This exothermic transformation involves a 20% volume contraction and a significant increase in resistivity. The reversion of α′ to δ involves a large temperature hysteresis and begins just above room temperature. In an attempt to better understand the underlying thermodynamics and kinetics responsible for these unusual features, we are examining the δ/α' transformations in a Pu-0.6 wt% Ga alloy using differential scanning calorimetry (DSC) and resistometry. Both techniques indicate that the martensite start temperature is −120°C and the austenite start temperature is 35°C. The heat of transformation is approximately 3 kJ/mole. During the α ′ → δ reversion, “spikes” and “steps” are observed in DSC and resistometry scans, respectively. These spikes and steps are periodic, and their periodicity with respect to temperature does not vary with heating rate. With an appropriate annealing cycle, including a “rest” at room temperature, these spikes and steps can be reproduced through many thermal cycles of a single sample.

scholarly journals Experimental Studies on Frozen Soil

2021 ◽  
Author(s):  
Kshitij Gaur ◽  
Anil Kumar Sahu
Keyword(s):  
Room Temperature ◽  
Void Ratio ◽  
Experimental Studies ◽  
Soil Surface ◽  
Negative Temperature ◽  
Research Data ◽  
Frozen Soil ◽  
Soil Parameters ◽  
Frozen Soils ◽  
A Site

Abstract Various studies have been carried out for soils at normal room temperature but the studies on frozen soils are meagre. For every construction, soil investigation is the most important and the primary step for a site. For constructions at normal room temperature, there is plenty of experimentation and research data on soil is available. But lack of research data for colder regions, where the ambient temperature is below zero degrees Celsius for most of the time. It is therefore the need to study soil under the iced condition to get a better idea about the behaviour of frozen soils. There is little research on the construction and mechanical behaviour of frozen soil but no study on the very basic parameters like void ratio, bulk density, porosity, and the degree of freezing and how these parameters change as the soil temperature changes from normal room temperature to negative values. The main emphasis is on the study and experimentation of frozen soil and the formulation of different relationships between individual soil parameters at various temperatures. The methodology used is to model the soil surface (open grounds in colder regions) by taking sand as the soil after sieving. The model samples are taken into beakers with different bulk densities to replicate real site conditions in the freezer. Then by calculating factors like density, porosity, void ratio, etc at negative temperature (-5, -10, -15, -20 degree Celsius) and forming a relationship with the same parameters as that on room temperature. The experimental data obtained is used in “Eureqa software” that will utilize the input so provided and will find mathematical relations that exist in the soil parameters.

scholarly journals Experimental Studies on Frozen Soil

2021 ◽  
Author(s):  
Kshitij Gaur ◽  
Anil Kumar Sahu
Keyword(s):  
Room Temperature ◽  
Void Ratio ◽  
Experimental Studies ◽  
Soil Surface ◽  
Negative Temperature ◽  
Research Data ◽  
Frozen Soil ◽  
Soil Parameters ◽  
Frozen Soils ◽  
A Site

Abstract Various studies have been carried out for soils at normal room temperature but the studies on frozen soils are meagre. For every construction, soil investigation is the most important and the primary step for a site. For constructions at normal room temperature, there is plenty of experimentation and research data on soil is available. But lack of research data for colder regions, where the ambient temperature is below zero degrees Celsius for most of the time. It is therefore the need to study soil under the iced condition to get a better idea about the behaviour of frozen soils. There is little research on the construction and mechanical behaviour of frozen soil but no study on the very basic parameters like void ratio, bulk density, porosity, and the degree of freezing and how these parameters change as the soil temperature changes from normal room temperature to negative values. The main emphasis is on the study and experimentation of frozen soil and the formulation of different relationships between individual soil parameters at various temperatures. The methodology used is to model the soil surface (open grounds in colder regions) by taking sand as the soil after sieving. The model samples are taken into beakers with different bulk densities to replicate real site conditions in the freezer. Then by calculating factors like density, porosity, void ratio, etc at negative temperature (-5, -10, -15, -20 degree Celsius) and forming a relationship with the same parameters as that on room temperature. The experimental data obtained is used in “Eureqa software” that will utilize the input so provided and will find mathematical relations that exist in the soil parameters.

Wordly Corrasions: Philology and Narrative inWorstward Ho

2017 ◽  
Vol 26 (1) ◽  
pp. 53-68
Author(s):  
Mark Byron
Keyword(s):  
First Principles ◽  
Alexander Pope ◽  
Literary Texts ◽  
Water Ice ◽  
Primary Documents ◽  
Land Farming ◽  
King James Bible ◽  
A Site ◽  
Thomas Browne ◽  
Geological Formations

Scholarly research over the last twenty years has marked a profound shift in the understanding of Beckett's sources, his methods of composition, and his attitudes towards citation and allusion in manuscript documents and published texts. Such landmark studies as James Knowlson's biography, Damned to Fame (1996), and John Pilling's edition of the Dream Notebook (1999), and the availability of primary documents such as Beckett's reading notes at Reading and Trinity libraries, opened the way for a generation of work rethinking Beckett's textual habitus. Given this profound reappraisal of Beckett's material processes of composition, this paper seeks to show that Beckett's late prose work, Worstward Ho, represents a profound mediation on writing, self-citation, and habits of allusion to the literary canon. In its epic gestures, it reorients the heavenly aspiration of Dante's Commedia earthwards, invoking instead the language of agriculture, geology and masonry in the process of creating and decreating its imaginative space. Beckett's earthy epic invokes and erodes the first principles of narrative by way of philology as well as by means of deft reference to literary texts and images preoccupied with land, farming, and geological formations. This process is described in the word corrasion, a geological term referring to the erosion of rock by various forms of water, ice, snow and moraine. Textual excursions into philology in Worstward Ho also unearth the strata comprising Beckett's corpus (in particular Imagination Dead Imagine, The Lost Ones, and Ill Seen Ill Said), as well as the rock or canon upon which his own literary production is built. A close reading of Worstward Ho turns up a number of shrewd allusions to the King James Bible and Thomas Browne, as one might expect, but also perhaps surprisingly sustained affinities with the literary sensibilities of Alexander Pope and the poetry of S. T. Coleridge. The more one digs, the more Beckett's ‘little epic’ seems to become one of earthworks, bits of pipe, and masonry, a site and record of literary sedimentation.

Intrinsic doping limit and defect-assisted luminescence in Cs4PbBr6

2019 ◽  
Author(s):  
Young-Kwang Jung ◽  
Joaquin Calbo ◽  
Ji-Sang Park ◽  
Lucy D. Wahlley ◽  
Sunghyun Kim ◽  
...  
Keyword(s):  
First Principles ◽  
Room Temperature ◽  
Stokes Shift ◽  
Green Luminescence ◽  
Counter Ions ◽  
Self Consistent ◽  
Deep Ultraviolet ◽  
Halide Perovskite ◽  
Related Compounds ◽  
Level Analysis

Cs<sub>4</sub>PbBr<sub>6 </sub>is a member of the halide perovskite family that is built from isolated (zero-dimensional) PbBr<sub>6</sub><sup>4-</sup> octahedra with Cs<sup>+</sup> counter ions. The material exhibits anomalous optoelectronic properties: optical absorption and weak emission in the deep ultraviolet (310 - 375 nm) with efficient luminescence in the green region (~ 540 nm). Several hypotheses have been proposed to explain the giant Stokes shift including: (i) phase impurities; (ii) self-trapped exciton; (iii) defect emission. We explore, using first-principles theory and self-consistent Fermi level analysis, the unusual defect chemistry and physics of Cs<sub>4</sub>PbBr<sub>6</sub>. We find a heavily compensated system where the room-temperature carrier concentrations (< 10<sup>9</sup> cm<sup>-3</sup>) are more than one million times lower than the defect concentrations. We show that the low-energy Br-on-Cs antisite results in the formation of a polybromide (Br<sub>3</sub>) species that can exist in a range of charge states. We further demonstrate from excited-state calculations that tribromide moieties are photoresponsive and can contribute to the observed green luminescence. Photoactivity of polyhalide molecules is expected to be present in other halide perovskite-related compounds where they can influence light absorption and emission. <br>

Intrinsic doping limit and defect-assisted luminescence in Cs4PbBr6

2019 ◽  
Author(s):  
Young-Kwang Jung ◽  
Joaquin Calbo ◽  
Ji-Sang Park ◽  
Lucy D. Wahlley ◽  
Sunghyun Kim ◽  
...  
Keyword(s):  
First Principles ◽  
Room Temperature ◽  
Stokes Shift ◽  
Green Luminescence ◽  
Counter Ions ◽  
Self Consistent ◽  
Deep Ultraviolet ◽  
Halide Perovskite ◽  
Related Compounds ◽  
Level Analysis

Cs<sub>4</sub>PbBr<sub>6 </sub>is a member of the halide perovskite family that is built from isolated (zero-dimensional) PbBr<sub>6</sub><sup>4-</sup> octahedra with Cs<sup>+</sup> counter ions. The material exhibits anomalous optoelectronic properties: optical absorption and weak emission in the deep ultraviolet (310 - 375 nm) with efficient luminescence in the green region (~ 540 nm). Several hypotheses have been proposed to explain the giant Stokes shift including: (i) phase impurities; (ii) self-trapped exciton; (iii) defect emission. We explore, using first-principles theory and self-consistent Fermi level analysis, the unusual defect chemistry and physics of Cs<sub>4</sub>PbBr<sub>6</sub>. We find a heavily compensated system where the room-temperature carrier concentrations (< 10<sup>9</sup> cm<sup>-3</sup>) are more than one million times lower than the defect concentrations. We show that the low-energy Br-on-Cs antisite results in the formation of a polybromide (Br<sub>3</sub>) species that can exist in a range of charge states. We further demonstrate from excited-state calculations that tribromide moieties are photoresponsive and can contribute to the observed green luminescence. Photoactivity of polyhalide molecules is expected to be present in other halide perovskite-related compounds where they can influence light absorption and emission. <br>

Mechanical Alloying Behavior in the Nb-Si, Ta-Si, and Nb-Ta-Si Systems

1988 ◽  
Vol 133 ◽  
Author(s):  
K. S. Kumar ◽  
S. K. Mannan
Keyword(s):  
High Temperature ◽  
Mechanical Alloying ◽  
Mechanical Milling ◽  
Room Temperature ◽  
Crystalline Compound ◽  
X Ray Diffraction ◽  
X Ray ◽  
Β Phase ◽  
Α Phase

ABSTRACTThe mechanical alloying behavior of elemental powders in the Nb-Si, Ta-Si, and Nb-Ta-Si systems was examined via X-ray diffraction. The line compounds NbSi2 and TaSi2 form as crystalline compounds rather than amorphous products, but Nb5Si3 and Ta5Si3, although chemically analogous, respond very differently to mechanical milling. The Ta5Si3 composition goes directly from elemental powders to an amorphous product, whereas Nb5Si3 forms as a crystalline compound. The Nb5Si3 compound consists of both the tetragonal room-temperature α phase (c/a = 1.8) and the tetragonal high-temperature β phase (c/a = 0.5). Substituting increasing amounts of Ta for Nb in Nb5Si3 initially stabilizes the α-Nb5Si3 structure preferentially, and subsequently inhibits the formation of a crystalline compound.

scholarly journals Structural and physical properties of 99 complex bulk chalcogenides crystals using first-principles calculations

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sahib Hasan ◽  
Khagendra Baral ◽  
Neng Li ◽  
Wai-Yim Ching
Keyword(s):  
Mechanical Properties ◽  
Physical Properties ◽  
First Principles ◽  
Experimental Studies ◽  
First Principles Calculations ◽  
Chalcogenide Semiconductors ◽  
Optical And Mechanical Properties ◽  
Very Large Database ◽  
Unique Composition ◽  
Fundamental Physical

AbstractChalcogenide semiconductors and glasses have many applications in the civil and military fields, especially in relation to their electronic, optical and mechanical properties for energy conversion and in enviormental materials. However, they are much less systemically studied and their fundamental physical properties for a large class chalcogenide semiconductors are rather scattered and incomplete. Here, we present a detailed study using well defined first-principles calculations on the electronic structure, interatomic bonding, optical, and mechanical properties for 99 bulk chalcogenides including thirteen of these crytals which have never been calculated. Due to their unique composition and structures, these 99 bulk chalcogenides are divided into two main groups. The first group contains 54 quaternary crystals with the structure composition (A2BCQ4) (A = Ag, Cu; B = Zn, Cd, Hg, Mg, Sr, Ba; C = Si, Ge, Sn; Q = S, Se, Te), while the second group contains scattered ternary and quaternary chalcogenide crystals with a more diverse composition (AxByCzQn) (A = Ag, Cu, Ba, Cs, Li, Tl, K, Lu, Sr; B = Zn, Cd, Hg, Al, Ga, In, P, As, La, Lu, Pb, Cu, Ag; C = Si, Ge, Sn, As, Sb, Bi, Zr, Hf, Ga, In; Q = S, Se, Te; $$\hbox {x} = 1$$ x = 1 , 2, 3; $$\hbox {y} = 0$$ y = 0 , 1, 2, 5; $$\hbox {z} = 0$$ z = 0 , 1, 2 and $$\hbox {n} = 3$$ n = 3 , 4, 5, 6, 9). Moreover, the total bond order density (TBOD) is used as a single quantum mechanical metric to characterize the internal cohesion of these crystals enabling us to correlate them with the calculated properties, especially their mechanical properties. This work provides a very large database for bulk chalcogenides crucial for the future theoretical and experimental studies, opening opportunities for study the properties and potential application of a wide variety of chalcogenides.

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