| 1. |
- Abdel-Hafiez, Mahmoud, et al.
(författare)
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Pressure-induced reentrant transition in NbS3 phases : Combined Raman scattering and x-ray diffraction study
- 2019
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 99:23
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Tidskriftsartikel (refereegranskat)abstract
- We report the evolution of charge density wave states under pressure for two NbS3 phases: triclinic (phase I) and monoclinic (phase II) at room temperature. Raman and x-ray diffraction (XRD) techniques are applied. The x-ray studies on the monoclinic phase under pressure show a compression of the lattice at different rates below and above similar to 7 GPa but without a change in space group symmetry. The Raman spectra of the two phases evolve similarly with pressure; all peaks almost disappear in the similar to 6-8 GPa range, indicating a transition from an insulating to a metallic state, and peaks at new positions appear above 8 GPa. The results suggest suppression of the ambient charge-density waves and their subsequent recovery with new orderings above 8 GPa.
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| 2. |
- Bandyopadhyay, Arka, et al.
(författare)
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8-16-4 graphyne : Square-lattice two-dimensional nodal line semimetal with a nontrivial topological Zak index
- 2021
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Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 103:7
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Tidskriftsartikel (refereegranskat)abstract
- An unprecedented graphyne allotrope with square symmetry and nodal line semimetallic behavior has been proposed in the two-dimensional (2D) realm. The emergence of the Dirac loop around the high-symmetry points in the presence of both the inversion and time-reversal symmetries is a predominant feature of the electronic band structure of this system. Besides, the structural stability in terms of the dynamic, thermal, and mechanical properties has been critically established for the system. Following the exact analytical model based on the realspace renormalization group scheme and tight-binding approach, we have inferred that the family of 2D nodal line semimetals with square symmetry can be reduced to a universal four-level system in the low-energy limit. This renormalized lattice indeed explains the underlying mechanism responsible for the fascinating emergence of 2D square nodal line semimetals. Besides, the analytical form of the generic dispersion relation of these systems is well supported by our density-functional theory results. Finally, the nontrivial topological properties have been explored for the predicted system without breaking the inversion and time-reversal symmetry of the lattice. We have obtained that the edge states are protected by the nonvanishing topological index, i.e., Zak phase.
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| 3. |
- Gallego-Parra, Samuel, et al.
(författare)
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Pressure-induced order-disorder transitions in beta-In2S3 : an experimental and theoretical study of structural and vibrational properties
- 2021
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 23:41, s. 23625-23642
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Tidskriftsartikel (refereegranskat)abstract
- This joint experimental and theoretical study of the structural and vibrational properties of beta-In2S3 upon compression shows that this tetragonal defect spinel undergoes two reversible pressure-induced order-disorder transitions up to 20 GPa. We propose that the first high-pressure phase above 5.0 GPa has the cubic defect spinel structure of alpha-In2S3 and the second high-pressure phase (phi-In2S3) above 10.5 GPa has a defect alpha-NaFeO2-type (R3m) structure. This phase, related to the NaCl structure, has not been previously observed in spinels under compression and is related to both the tetradymite structure of topological insulators and to the defect LiTiO2 phase observed at high pressure in other thiospinels. Structural characterization of the three phases shows that alpha-In2S3 is softer than beta-In2S3 while phi-In2S3 is harder than beta-In2S3. Vibrational characterization of the three phases is also provided, and their Raman-active modes are tentatively assigned. Our work shows that the metastable alpha phase of In2S3 can be accessed not only by high temperature or varying composition, but also by high pressure. On top of that, the pressure-induced beta-alpha-phi sequence of phase transitions evidences that beta-In2S3, a BIII2XV3 compound with an intriguing structure typical of A(II)BIII(2)XVI(4) compounds (intermediate between thiospinels and ordered-vacancy compounds) undergoes: (i) a first phase transition at ambient pressure to a disordered spinel-type structure (alpha-In2S3), isostructural with those found at high pressure and high temperature in other BIII2XV3 compounds; and (ii) a second phase transition to the defect alpha-NaFeO2-type structure (phi-In2S3), a distorted NaCl-type structure that is related to the defect NaCl phase found at high pressure in A(II)BIII(2)XVI(4) ordered-vacancy compounds and to the defect LiTiO2-type phase found at high pressure in A(II)BIII(2)XVI(4) thiospinels. This result shows that In2S3 (with its intrinsic vacancies) has a similar pressure behaviour to thiospinels and ordered-vacancy compounds of the A(II)BIII(2)XVI(4) family, making beta-In2S3 the union link between such families of compounds and showing that group-13 thiospinels have more in common with ordered-vacancy compounds than with oxospinels and thiospinels with transition metals.
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| 4. |
- Ji, Cheng, et al.
(författare)
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Crystallography of low Z material at ultrahigh pressure : Case study on solid hydrogen
- 2020
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Ingår i: Matter and Radiation at Extremes. - : American Institute of Physics (AIP). - 2468-2047 .- 2468-080X. ; 5:3
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Tidskriftsartikel (refereegranskat)abstract
- Diamond anvil cell techniques have been improved to allow access to the multimegabar ultrahigh-pressure region for exploring novel phenomena in condensed matter. However, the only way to determine crystal structures of materials above 100 GPa, namely, X-ray diffraction (XRD), especially for low Z materials, remains nontrivial in the ultrahigh-pressure region, even with the availability of brilliant synchrotron X-ray sources. In this work, we perform a systematic study, choosing hydrogen (the lowest X-ray scatterer) as the subject, to understand how to better perform XRD measurements of low Z materials at multimegabar pressures. The techniques that we have developed have been proved to be effective in measuring the crystal structure of solid hydrogen up to 254 GPa at room temperature [C. Ji et al., Nature 573, 558–562 (2019)]. We present our discoveries and experiences with regard to several aspects of this work, namely, diamond anvil selection, sample configuration for ultrahigh-pressure XRD studies, XRD diagnostics for low Z materials, and related issues in data interpretation and pressure calibration. We believe that these methods can be readily extended to other low Z materials and can pave the way for studying the crystal structure of hydrogen at higher pressures, eventually testing structural models of metallic hydrogen.
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| 5. |
- Ji, Cheng, et al.
(författare)
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Ultrahigh-pressure isostructural electronic transitions in hydrogen
- 2019
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 573:7775, s. 558-562
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Tidskriftsartikel (refereegranskat)abstract
- High-pressure transitions are thought to modify hydrogen molecules to a molecular metallic solid and finally to an atomic metal(1), which is predicted to have exotic physical properties and the topology of a two-component (electron and proton) superconducting superfluid condensate(2,3). Therefore, understanding such transitions remains an important objective in condensed matter physics(4,5). However, measurements of the crystal structure of solid hydrogen, which provides crucial information about the metallization of hydrogen under compression, are lacking for most high-pressure phases, owing to the considerable technical challenges involved in X-ray and neutron diffraction measurements under extreme conditions. Here we present a single-crystal X-ray diffraction study of solid hydrogen at pressures of up to 254 gigapascals that reveals the crystallographic nature of the transitions from phase I to phases III and IV. Under compression, hydrogen molecules remain in the hexagonal close-packed (hcp) crystal lattice structure, accompanied by a monotonic increase in anisotropy. In addition, the pressure-dependent decrease of the unit cell volume exhibits a slope change when entering phase IV, suggesting a second-order isostructural phase transition. Our results indicate that the precursor to the exotic two-component atomic hydrogen may consist of electronic transitions caused by a highly distorted hcp Brillouin zone and molecular-symmetry breaking.
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| 6. |
- Kyriakidis, Miltos, et al.
(författare)
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The indirect costs assessment of railway incidents and their relationship to human error : The case of Signals Passed at Danger
- 2019
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Ingår i: Journal of Rail Transport Planning & Management. - : Elsevier. - 2210-9706 .- 2210-9714. ; 9, s. 34-45
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Tidskriftsartikel (refereegranskat)abstract
- The majority of railway incidents result neither in passenger nor operators harm, nor they lead to any severe damage on the rolling stock or the infrastructure. Nevertheless, such incidents result in financial loses, broadly known as indirect costs, which are difficult to identify, isolate, evaluate, and quantify. This paper introduces a framework to quantify the indirect costs in railway operations. Furthermore, as degraded human performance remains a major contributor to operational errors and railway incidents, this study explores for associations between the indirect costs and the factors that affect and contribute to degraded human performance. The framework was implemented in the calculation of the Category A1 Signals Passed at Danger (SPADs) indirect costs. Data was obtained from two UK train operators, while the associated human performance was analysed using the Railway-Performance Shaping Factors (R-PSFs) taxonomy. Employing Spearman's rank order correlation and Fisher's exact statistical tests the associations between R-PSFs and indirect costs were reviewed. Results show significant correlations between the R-PSFs and indirect costs, but only if the importance and severity of every individual R-PSFs is considered. We expect our findings to aid the relevant stakeholders on their efforts to make better decisions on improving safety performance of railway operations.
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| 7. |
- Majumdar, Arnab, et al.
(författare)
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Drastic reduction of thermal conductivity in hexagonal AX (A = Ga, In & Tl, X = S, Se & Te) monolayers due to alternative atomic configuration
- 2021
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Ingår i: Nano Energy. - : Elsevier. - 2211-2855 .- 2211-3282. ; 88
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Tidskriftsartikel (refereegranskat)abstract
- Several two-dimensional chalcogenide materials have been in the limelight in the recent past for their promising thermoelectric properties. It is well established that the thermoelectric performance of materials improves on reducing the physical dimensionality of the system. Two-dimensional hexagonal chalcogen (S, Se and Te) bearing compounds of Ga, In and Tl have already been studied extensively in literature. But in those phases, the group-13 non-chalcogen atoms occupy the two inner planes while the chalcogens occupy the two outer planes of the unit cell. In this work, we have proposed the alternate arrangement in which the chalcogen atoms occupy the two inner planes while the group-13 atoms occupy the two outer planes of the unit cell. Unprecedentedly, this alternate arrangement shows much lower thermal conductivity that leads to superior thermoelectric performance. In this work we have studied in details the thermoelectric properties of hexagonal AX (A = Ga, In & Tl, X = S, Se & Te) monolayers and compare the results having both the atomic arrangements. The very low lattice thermal conductivity of this new arrangement is due to the outermost valence s-orbital lone pair of the chalcogens which leads to enhanced anharmonicity. We have explained these results from the anti-crossing of the phonon branches as well. The electronic, dynamical, thermodynamical and elastic properties have also been studied. We think that these results should have significant impact on the synthesis of high-performance thermoelectric materials based on chalcogenides of gallium, indium and thallium.
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| 8. |
- Majumdar, Arnab, et al.
(författare)
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Emerging piezochromism in lead free alkaline earth chalcogenide perovskite AZrS(3) (A = Mg, Ca, Sr and Ba) under pressure
- 2020
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 8:46, s. 16392-16403
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Tidskriftsartikel (refereegranskat)abstract
- Hydrostatic pressure is an effective tool that can give rise to novel crystal structures and physical properties. It has proven to be an alternative to chemical pressure. Therefore new functional materials with intriguing properties can be designed by exerting external pressure. Metal chalcogenide perovskites are a class of perovskites that have several advantages, namely high stability against moisture and light induced degradation along with nontoxic elemental composition. In this letter, we have used first principles methods to study the structural, electronic and optical properties of AZrS(3) where A = Mg, Ca, Sr and Ba upon compression. Upon being compressed, the direct band gaps decrease to desired values which can enable this class of zirconium based chalcogenide perovskites to be used in tandem solar cells. The mobility of the charge carriers increases with pressure as the effective masses decrease. Piezochromism is seen to exist upon compression which can be verified from the modifications in the optical absorption spectra. This work elucidates the effects of pressure on the sensitive tuning of properties of zirconium based chalcogenide perovskites, which can have significant photovoltaic applications.
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| 9. |
- Majumdar, Arnab, et al.
(författare)
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Emerging piezochromism in transparent lead free perovskite Rb3X2I9 (X=Sb, Bi) under compression : A comparative theoretical insight
- 2020
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 128:4, s. 045102-
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Tidskriftsartikel (refereegranskat)abstract
- Hydrostatic pressure has proven to be an alternative tool to chemical pressure to tune the crystal structure and physical and chemical properties, paving the way for a novel functional materials design. Halide perovskites consist of a large family of perovskites, with tremendous potential for energy applications. Their soft lattices and distinct behavior under pressure make them necessary to be studied under compressed conditions. Ternary antimony halides are one such class of perovskites that act as an alternative to lead (Pb) halide perovskites due to the lesser toxicity of Sb/Bi in comparison with Pb. In this letter, we have theoretically envisaged the effects of compression via hydrostatic pressure on the structural, electronic, and optical properties of Rb3X2I9, where X=Sb and Bi-. The bandgaps not only decrease but are also direct in the desired pressure range. The calculated effective masses decrease with pressure, thereby indicating higher mobility of the charge carriers in the compressed material. The presence of piezochromism has also been confirmed from the variation of optical properties under hydrostatic compression. Our investigations shed light on the pressure dependent sensitive tuning of electronic and optical properties of Rb3Bi2I9 and Rb3Sb2I9, rendering these materials to have significant photovoltaic applications.
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| 10. |
- Majumdar, Arnab, et al.
(författare)
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High exothermic dissociation in van der Waals like hexagonal two dimensional nitrogene from first-principles molecular dynamics
- 2020
-
Ingår i: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 529
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Tidskriftsartikel (refereegranskat)abstract
- Mono and multilayered two dimensional (2D) nitrogene in which nitrogen atoms are single bonded are studied for energy applications. The structures are observed to be dynamically and thermally stable at room temperature but dissociate into triple bonded N-2 molecules at higher temperatures. From ab initio molecular dynamics simulations, the dissociation temperature is found to be decreasing with increasing number of layers (1500 K for single layer and 500 K for six layers). The energy released for the different layered cases is large due to the energy difference between single and triple-bonded nitrogen (similar to 0.88 - 1.8 eV/atom). Significantly high energy densities calculated for the multilayered structures (similar to 6 - 12.3 kJ/gm) can secure these materials an important position amongst non-nuclear and inorganic high energy density materials known today. We believe that this work will shed light on synthesizing next generation non-nuclear environmentally clean high energy density materials using multi-layer nitrogene that detonate at not very high temperatures.
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| 11. |
- Majumdar, Arnab, et al.
(författare)
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Interplay of charge density wave and multiband superconductivity in layered quasi-two-dimensional materials : The case of 2H-NbS2 and 2H-NbSe2
- 2020
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Ingår i: Physical Review Materials. - : American Physical Society (APS). - 2475-9953. ; 4:8
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Tidskriftsartikel (refereegranskat)abstract
- Despite intense efforts on all known quasi-two-dimensional superconductors, the origin and exact boundary of the electronic orderings, particularly charge density waves and superconductivity, are still attractive problems with several open questions. Here, in order to reveal how the superconducting gap evolves, we report on high quality complementary measurements of magneto-optical imaging, specific heat, magnetic susceptibility, resis-tivity measurements, Andreev spectroscopy, and London penetration depth lambda(ab)(T) measurements supplemented with theoretical calculations for 2H-NbSe2 and 2H-NbS2 single crystals. The temperature dependence of lambda(ab)(T) calculated from the lower critical field and Andreev spectroscopy can be well described by using a two-band model with s-wave-like gaps. The effect of pressure on the superconducting gap of both systems illustrates that both bands are practically affected. Upon compression, the Fermi surfaces do not change significantly, and the nesting remains almost unaffected compared to that at ambient condition. However, a strong bending in the upper critical fields (H-c2) curves is obtained under pressure and support the presence of a strong Pauli paramagnetic effect. In NbSe2, using a two-band model with s-wave-like gaps, the temperature dependence H-c2(T) can be properly described. In contrast to that, the behavior of H-c2 for NbS2 is ruled by the spin paramagnetic effect. The estimated values of the penetration depth at T = 0 K confirm that NbSe2 and NbS2 superconductors depart from a Uemura-style relationship between Tc with lambda(-2)(ab) (T ), the in-plane superconducting penetration depth.
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| 12. |
- Majumdar, Arnab, et al.
(författare)
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Pressure induced structural phase transition and piezochromism in photovoltaic sillen compounds PbBiO2X (X = Cl, Br & I)
- 2022
-
Ingår i: APPLIED MATERIALS TODAY. - : Elsevier. - 2352-9407. ; 26
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrostatic pressure is an effective and clean method that can give rise to the emergence of novel crystal structures and physical properties. Thus, hydrostatic pressure can be used for designing new functional materials. Sillen materials or PbBiO2X (X = Cl, Br & I) are a class of materials which have gained considerable interest in the field of ferroelectrics, photocatalysis, etc . In this work, we have used first principles methods to predict the crystal structure and phase of sillen materials at different pressure points from 0 to 50 GPa. It was then followed by the study of their structural, electronic and optical properties upon compression. Upon compression, the band gaps decreased within a particular phase and showed kinks on phase transitions. In the compressed states, the band gaps are in the suitable range to be used in the visible range of the spectrum for photovoltaic properties. Piezochromism is also reported upon compression as can been seen from the changes in the optical absorption spectra. This work should remove any confusion with regards to the responsible phase at different pressures, and the possible existence of new phases with the respective band gaps should pave the way for future experimental works on photocatalysis and other energy applications. (c) 2022 The Author(s). Published by Elsevier Ltd.& nbsp;
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| 13. |
- Majumdar, Arnab, et al.
(författare)
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Purely ionically bonded cation paving the way to ultralow thermal conductivity and large thermoelectric figure of merit in Ruddlesden-Popper perovskite Cs2SnI2Br2
- 2024
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Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 36:34
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Tidskriftsartikel (refereegranskat)abstract
- Lower dimensional materials have gained quite a bit of popularity in the last few decades. Perovskite materials have been studied extensively for their photovoltaic properties. But for large scale application of photovoltaic materials, the thermal properties need to be studied. In this work, using first principles calculations, we have studied the thermal conductivity and thermoelectric performance of quasi two-dimensional (2D) Ruddlesden-Popper phase of perovskite, Cs2SnI2Br2. The Cs atoms are found to be ionically bonded to the halogens leading to low elastic constants and hence give rise to weak bonding. The large anharmonicity in this material causes the lattice thermal conductivity to be ultralow having a value of 0.30 Wm(-1)K-1 at 300 K and therefore the thermoelectric figure of merit has been found to be high with a maximum value of 2.08 at 600 K. This lead-free 2D perovskite can be the precursor to a wide variety of similar materials with ultralow thermal conductivity.
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| 14. |
- Majumdar, Arnab, et al.
(författare)
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Ultralow Thermal Conductivity and High Thermoelectric Figure of Merit in Two-Dimensional Thallium Selenide
- 2020
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:9, s. 9315-9325
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Tidskriftsartikel (refereegranskat)abstract
- Several selenides have been studied as potential thermoelectric materials in the past. Thermoelectric performance improves on reducing the dimension of the system. Following these notions, we studied three hexagonal two-dimensional phases of thallium selenide for promising thermoelectric performance by using first-principles techniques. Their dynamical and mechanical stabilities have been shown. The band gaps using different approximations of calculations have been reported and are in the range that can render these materials to show optimal thermoelectric performance. The lattice thermal conductivity is ultralow between 0.088 and 0.429 W m(-1) K-1 at 900 K. High thermoelectric performance has been predicted in the systems with the figure of merit reaching magnitudes of similar to 0.5-1.94 between 300 and 900 K. The high thermoelectric performance results from an ultralow thermal conductivity arising due to the strong lattice anharmonicity. These results can have significant impact on the synthesis of high performance thermoelectric materials based on thallium selenide.
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| 15. |
- Singh, Sarbjeet, et al.
(författare)
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Incorporating Human Reliability Analysis to enhance Maintenance Audits : The Case of Rail Bogie Maintenance
- 2017
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Ingår i: International Journal of Prognostics and Health Management. - USA : Prognostics and Health Management (PHM) Society. - 2153-2648. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Human errors occurring during railway maintenance activities can significantly reduce the availability of equipment. Identification of potential human errors, their causes and prediction of the associated probabilities are important stages in order to manage such errors. This paper investigates the probability of human error during the maintenance of railway bogies. A case study examines technicians performing maintenance on the disc brake assembly unit, wheel set, and bogie frame under various error producing conditions in a railway maintenance workshop in Luleå, Sweden. The Human Error Assessment and Reduction Technique (HEART) is employed to determine the probability of human error occurring during each of the maintenance tasks, while fault tree analysis is used to define the potential errors throughout the maintenance process. The probability of a technician committing an error during the maintenance of the disc brake assembly, wheel set, and bogie frame is found to be 0.20, 0.039 and 0.021 respectively, with the human error probability (HEP) for the entire bogie 0.24. Time pressure, ability to detect and perceive problems, over-riding information, the need to make decisions and mismatches between the operator and designer’s model turn out to be major contributors to human error. These findings can help maintenance management personnel to better understand the error producing conditions that may lead to errors and in turn serve as an input to modify policies and guidelines for railway maintenance tasks.
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| 16. |
- Tsuppayakorn-aek, Prutthipong, et al.
(författare)
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Superconducting state of the van der Waals layered PdH2 structure at high pressure
- 2023
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 48:44, s. 16769-16778
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Tidskriftsartikel (refereegranskat)abstract
- We report structural and superconducting transitions in layered van der Waals (vdW) palladium dihydride (PdH2) calculated under high-pressure compression. PdH2 has a Hexagonal Closed-Packed (HCP) structure with a space group of P63mc, and has a super-conducting transition temperature of 24 K at ambient pressure. At 15 GPa, the crystalline to vdW layered structural transition occurs, while the superconductivity remains. On com-pressing from 15 to 50 GPa, the Tc increased abnormally by 3.5 K. It is found that the superconducting critical temperature of P63mc PdH2 is determined by the out-of-plane interlayer breathing vibrational mode. As a vdW layered metal hydride superconductor, PdH2 provides a platform to study hydride superconductivity in such kinds of materials. (c) 2023 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).
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| 17. |
- Zidane, Mustapha, et al.
(författare)
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Determination and comparison of the electrical and thermal transport properties of BCC and FCC Fe-Ni based ternary alloys in the Earth's inner core
- 2022
-
Ingår i: JOURNAL OF EARTH SYSTEM SCIENCE. - : Springer Nature. - 2347-4327 .- 0973-774X. ; 131:4
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Tidskriftsartikel (refereegranskat)abstract
- The Earth's core contains, in addition to iron, 5-10% nickel and many light elements such as C, O, Si and S, among others. For this work, we consider binary Fe-Ni alloys with 10% Ni as host material, doped with light elements as impurity atoms. The phases considered for the Fe-Ni host alloy are face-centered cubic (fcc) and body-centred cubic (bcc). At different concentrations of 2.5-50%, the impurity atoms C, O, Si and S were placed in the host Fe-Ni alloy to create ternary alloys. The resulting ternary systems are exposed to a pressure equivalent to that existing at the Earth's core. As shown by their formation energies, these alloys are stable and advantageous. The calculation of the resistivity of the impurities was performed with the help of the Kubo-Greenwood formula. Compared to fcc, in the case of bcc, electrical resistivities begin to saturate at about 30% of the atomic concentration of the impurities. Thermal conductivity was also determined from electrical resistivities calculated for varying concentrations and pressures according to Wiedemann-Franz law. In the case of compression, we observe a rise in thermal conductivity of about 1.5% of the core's internal pressure. The reported thermal conductivities support the notion of maintaining a convection-induced geodyanmo.
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| 18. |
- Zidane, Mustapha, et al.
(författare)
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Electrical and thermal transport properties of Fe-Ni based ternary alloys in the earth's inner core : An ab initio study
- 2020
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Ingår i: Physics of the Earth and Planetary Interiors. - : ELSEVIER. - 0031-9201 .- 1872-7395. ; 301
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Tidskriftsartikel (refereegranskat)abstract
- Besides iron, the Earth's core also contains 5-10% of nickel and several light elements such as H, C, N, O, Si and S. Fe-Ni alloys have been considered as the host material with 10% Ni. The impurity atoms which are comprised of the light elements have been incorporated at different concentrations in the host alloy, giving rise to ternary alloys. All these systems have been subjected to compression at pressures similar to that in the inner core of the Earth. The atomic concentration of the impurities has been varied from 2.5% to 50%. The formation enthalpies suggest that these ternary alloys are energetically favorable. The impurity resistivity is calculated using the Kubo-Greenwood formula. At approximately similar to 30% of atomic concentration of impurities, the electrical resistivities start to saturate. For lesser percentage of hydrogen, the impurity resistivity is in the same range as that of the rest. But once the concentration of hydrogen increases, the impurity resistivity becomes very high. Generally, the resistivities are seen to plummet with increasing pressure. Using the Wiedemann-Franz law, the thermal conductivities were also determined from the calculated electrical resistivities for both varying concentration and pressure. On compression, the thermal conductivities increased by approximately 5% in the inner core pressure range.
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| 19. |
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| 20. |
- Zidane, Mustapha, et al.
(författare)
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Thermophysical properties of helium and hydrogen mixtures under high pressure predicted by ab-initio calculations : Implications for Saturn and Jupiter planets
- 2022
-
Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 555, s. 111430-
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Tidskriftsartikel (refereegranskat)abstract
- The thermodynamic and physical properties of Helium (He) and Hydrogen (H) mixtures are crucial form an astrophysical perspective. Nowadays, it is well known that these two elements constitute roughly 95% of the matter in the solar system. The high-pressure equation of He state doped with H is calculated in the framework of density functional theory (DFT) for three crystallographic structures. Namely, the Body Centered Cubic (BCC), Face Centered Cubic (FCC), and hexagonal close packed (HCP) structures have been studied. The equations of state (EOS) are provided for the He0.90H0.10 and He0.70H0.30 mixtures and the energy of the same mixtures are calculated with the earlier structures. The band structure for pressures of 0, 75 and 150 GPa were estimated by our calculations for the presumed crystal structures in the case of pure He and He0.70H0.30 mixture for comparison. The k(x) - k(y) cuts of the Bloch Spectral Functions (BSF) are presented for the pure He and He0.70H0.30 mixture for the three structures to explore the impact of doping on electronic properties. In addition, electrical resistivity calculations of the mentioned structures were carried out for mixtures with 10, 15, 20 and 30% of H. At final stage, the enthalpy (Delta H) of these latest mixtures have been deduced for the three crystal structures.
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