| 1. |
- Ektarawong, A., et al.
(författare)
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Effect of thermally excited lattice vibrations on the thermodynamic stability of tungsten ditellurides WTe2 under high pressure: A first-principles investigation
- 2021
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Ingår i: Computational materials science. - : ELSEVIER. - 0927-0256 .- 1879-0801. ; 186
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Tidskriftsartikel (refereegranskat)abstract
- The thermodynamic stability as a function of pressure and temperature of three WTe2 polytypes, i. e., Td, 1T , and 2H phases, is examined using first-principles calculations, where the temperature-dependent contributions, arising particularly from the lattice vibrations, are derived from the quasiharmonic approximation. We find that the critical transition pressure to the 2H phase increases almost linearly with increasing temperature. Through the inspection of the phonon density of states, 2H-WTe2 is dynamically stable not only at high pressure, but also at zero pressure, indicating possible existence of 2H-WTe2 also at ambient conditions. On the other side, our results demonstrate that, at relevant temperature and pressure, the thermodynamic stability of 1T-WTe2 is comparable to that of Td-WTe2, and further analysis reveals substantial similarities in terms of structural behavior between Td-WTe2 and 1T-WTe2. These findings suggest not only that the two polytypes are likely to coexist in practical samples of WTe2 due probably to grains/regions either with tiny difference in stress, for example, or with different growth history, but also that the designation of 1T , having been regularly used to described the compound under pressure in the literature, might actually be a mixture of Td and 1T polytypes, whose WTe2 layers laterally slide via low transition barrier induced probably by the applied pressure, resulting in the splitting of (101) and (113) peaks as observed in the diffraction experiments.
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| 2. |
- Kotmool, K., et al.
(författare)
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High-Pressure Structural Transformation Pathway and Electronic Properties of AgGaTe2 : Ab Initio Evolutionary Structural Searching
- 2022
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:33, s. 14236-14244
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Tidskriftsartikel (refereegranskat)abstract
- We have used systematic ab initio evolutionary structural searching to uncover the high-pressure transformation pathway of a promising thermoelectric material, AgGaTe2. The global structures of the ternary Ag-Ga-Te system have been predicted up to 100 GPa. The known chalcopyrite phase at ambient pressure is validated by the searching method. The B3-like structure with the space group (s.g.) of P((4) over bar)m(2) exhibits a metastable one at a low-pressure range. The first structural phase transition is calculated at about 4 GPa, processing the I((4) over bar) (2)d phase to a B1-like phase (s.g. Pmma). Other predicted structures, Pmn2(1) and Pm phases, are potentially coexisting phases up to 30 GPa because of the slightly different enthalpy. This finding reasonably explains the ambiguous results in the previous experiments. The high-pressure phase beyond 30 GPa is proposed to be a short-range alloy of bcc-Te and B2-AgGa rather than a cation-disordered B2-like phase. The band gap of the I((4) over bar)(2)d phase is increased with increasing pressure, while the metastable P((4) over bar)(2)m(2) phase is a narrow band gap semiconductor. The electron-phonon coupling of the metallic phases of ternary IB-IIIA-VIA(2) compounds is derived for the first time in AgGaTe2. They exhibit superconductors with a maximum Tc of 2.4 K in the Pmma phase at 6 GPa. The findings of this work not only provide a clear explanation of the high-pressure transformation pathway of AgGaTe2 but also suggest promising electronic properties guiding further applications, especially in a thermometric device, of this material under high pressure.
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| 3. |
- Manotum, R., et al.
(författare)
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Effect of pressure on the structure stability, electronic structure and band gap engineering in Zn16O1S15
- 2018
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Ingår i: Computational Condensed Matter. - : Elsevier B.V.. - 2352-2143. ; 17
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Tidskriftsartikel (refereegranskat)abstract
- Crystal structures and high pressure structural phase transitions of Zn16O1S15 have been investigated using density functional theory calculation. The two candidate high pressure structures namely Wurtzite and Zincblende were examined for theirs stability and properties up to 20 GPa. The co-exist phase of both structure which occurred during the different film growth conditions was fully explained. Phonon dispersion and the Born criteria reveal that Zincblende is only stable up to 10 GPa. Besides, Wurtzite structure yield no imaginary phonon frequencies and also satisfy the elastic constants sufficiency condition up to 20 GPa which indicated that the co-exist phase would eventually become the single Wurtzite structure above 10 GPa. The electronic structure and PDOS were also fully investigated using HSE06. The multiple band gap energy and mid O-3 state between fundamental ZnS band gap was revealed for the first time. The pressure effect on their electronic structure has been investigated for possible applications in adjustable optoelectronic device.
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| 4. |
- Sukmas, W., et al.
(författare)
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Data-driven analysis of the rotational energy landscapes of an organic cation in a substituted alloy perovskite
- 2021
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Ingår i: Materials Advances. - : Royal Society of Chemistry. - 2633-5409. ; 2:7, s. 2366-2372
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Tidskriftsartikel (refereegranskat)abstract
- Lead-free hybrid organic-inorganic perovskites have recently emerged as excellent materials particularly in highly potential yet low-cost photovoltaic technologies. Calculations have previously suggested that CH3NH3BiSeI2 can be used as an alternative material for the highly studied CH3NH3PbI3 due to its eco-friendliness and comparable performance. Herein, with the aid of Euler angles, the interplay between the organic CH3NH3 (MA) cation and the inorganic BiSeI2 framework, obtained from first-principles calculations, is thoroughly scrutinised by means of the multidimensional total energy landscape. The highest peak of 17.9 meV per atom, protruding from the average plateau of 9 meV per atom within the four-dimensional topography, is equivalent to 208 K, the temperature at which the MA cations freely reorient. Moreover, the complexity of the angle-energy relationship is mitigated by exploiting a high-fidelity simulation based on deep learning. The deep artificial neural network of five hidden layers with 500 neurons, each fed by ten descriptors-three Euler angles and seven various bond lengths-predicts the total energies with an accuracy within the root mean square error of 0.39 ± 0.03 meV per atom for the test dataset. This novel statistical model in turn offers a tantalising promise to provide an accurate prediction of this materials energies, while diminishing the need for costly first-principles calculations. © The Royal Society of Chemistry.
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| 5. |
- Tsuppayakorn-aek, P., et al.
(författare)
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Bain Deformation Mechanism and Lifshitz Transition in Magnesium under High Pressure
- 2020
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Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlag. - 0370-1972 .- 1521-3951.
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Tidskriftsartikel (refereegranskat)abstract
- The body-centered cubic (bcc) to face-centered cubic (fcc) phase transition of magnesium is explained by Bain deformation using first-principles calculations. It is shown that the bcc structure transforms into the fcc structure at a pressure of 489 GPa. The electronic band structure of the bcc structure exhibits the Lifshitz transition. The projected density of states of the bcc structure displays the s–d hybridization near the Fermi energy under high pressure. This remarkable structural feature shows the unique pathway leading to a common bcc–fcc Bain deformation mechanism among alkaline-earth metals.
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| 6. |
- Tsuppayakorn-aek, P., et al.
(författare)
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Hydrogen-induced phase stability and phonon mediated-superconductivity in two-dimensional van der Waals Ti2C MXene monolayer
- 2023
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 25:3, s. 2227-2233
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we report the phase stability of the hydrogenated Ti2C MXene monolayer using an evolutionary algorithm based on density functional theory. We predict the existence of hexagonal Ti2CH, Ti2CH2, and Ti2CH4. The dynamic and energetic stabilities of the predicted structures are verified through phonon dispersion and formation energy, respectively. The electron-phonon coupling is carefully investigated by employing isotropic Eliashberg theory. The T-c values are 0.2 K, 2.3 K, and 9.0 K for Ti2CH, Ti2CH2, and Ti2CH4, respectively. The translation and libration adopted by stretch and bent vibrations contribute to the increasing T-c of Ti2CH4. The high-frequency hydrogen modes contribute to the critical temperature increase. Briefly, this work not only highlights the effect of H-content on the increments of T-c for Ti2CHx, but also demonstrates the first theoretical evidence of the existence of H-rich MXene in the example of Ti2CH4. Therefore, it potentially provides a guideline for developing hydrogenated 2D superconductive applications.
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| 7. |
- Tsuppayakorn-aek, P., et al.
(författare)
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Thermodynamic stability and superconductivity of tantalum carbides from first-principles cluster expansion and isotropic Eliashberg theory
- 2022
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Ingår i: Computational materials science. - : ELSEVIER. - 0927-0256 .- 1879-0801. ; 202
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Tidskriftsartikel (refereegranskat)abstract
- The phase stability of tantalum carbides, particularly cubic rocksalt TaCx and hexagonal Ta2Cx, where 0 ≤ x ≤ 1 due to the presence of vacancies on the C sites, is explored using a first-principles cluster-expansion method. Our results demonstrate that at 0 K, in addition to stoichiometric cubic TaC and hexagonal Ta2C both widely known in the literature, carbon-deficient face-centered orthorhombic TaC0.833 is identified as a thermodynamically stable phase in the binary Ta-C system. By investigating their vibrational and electronic properties, the three carbides are dynamically stable and are metallic. We further demonstrate, by adopting phonon mediated superconductivity based on the Bardeen-Cooper-Schrieffer theory, that cubic TaC, face-centered orthorhombic TaC0.833, and hexagonal Ta2C superconduct, whose transition temperatures are estimated by the Allen-Dynes equation to be 10.0 K, 6.8 K, and 1.4 K, respectively. The physical origin of superconductivity in these stable carbides are discussed and described, based on the detailed analysis of the materials electronic and phonon properties.
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