| 1. |
- Bovornratanaraks, Thipok, et al.
(författare)
-
Electronic topological transitions and mechanical properties of hafnium dioxide allotrope at high pressure : Evolutionary first-principles techniques
- 2023
-
Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 649
-
Tidskriftsartikel (refereegranskat)abstract
- Allotrope of HfO2 is explored by using first-principles evolutionary algorithm technique, based on density functional theory. The tetragonal structure with the space group of P4/nmm is demonstrated thermodynamically stable within the harmonic level. Arising particularly from the relative enthalpy, hafnium dioxide allotrope is taken into account in appraising the dynamic stability. Following this, the phonon calculations display that hafnium dioxide allotrope is dynamically stable under compressed conditions. Along with electronic properties, the band structure and density of states demonstrate that hafnium dioxide allotrope is semiconductor. Besides, the more significant change in the shape of density of states is observed when the increase in pressure, by adopting an effect of this electronic topological transition, resulting in the energy gap decreased monotonically. By inspecting their elastic constants and Vicker's hardness, the P4/nmm structure displayed the Vicker's hardness of 26.1 GPa at a pressure of 200 GPa. These findings suggest HfO2 is more likely to be attained experimentally and theoretically in metal oxides family.
|
|
| 2. |
- Bovornratanaraks, Thiti, et al.
(författare)
-
Ground-state structure of semiconducting and superconducting phases in xenon carbides at high pressure
- 2019
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- The 'missing Xe paradox' is one of the phenomena at the Earth's atmosphere. Studying the 'missing Xe paradox' will provide insights into a chemical reaction of Xe with C. We search the ground-state structure candidates of xenon carbides using the Universal Structure Predictor: Evolutionary Xtallography (USPEX) code, which has been successfully applied to a variety of systems. We predict that XeC2 is the most stable among the convex hull. We find that the I((4) over bar)2m structure of XeC2 is the semiconducting phase. Accurate electronic structures of tetragonal XeC2 have been calculated using a hybrid density functionals HSE06, which gives larger more accurate band gap than a GGA-PBE exchange-correlation functional. Specifically, we find that the I((4) over bar)2m structure of XeC2 is a dynamically stable structure at high pressure. We also predict that the P6/mmm structure of XeC2 is the superconducting phase with a critical temperature of 38 K at 200 GPa. The ground-state structure of xenon carbides is of critical importance for understanding in the missing Xe. We discuss the inference of the stable structures of XeC2. The accumulation of electrons between Xe and C led to the stability by investigating electron localization function (ELF).
|
|
| 3. |
- Bovornratanaraks, Thipok, et al.
(författare)
-
Semiconducting phase of hafnium dioxide under high pressure : a theoretical study by quasi-particle GW calculations
- 2021
-
Ingår i: Materials Research Express. - : Institute of Physics Publishing (IOPP). - 2053-1591. ; 8:10
-
Tidskriftsartikel (refereegranskat)abstract
- The phase stability of the hafnium dioxide compounds HfO2, a novel material with a wide range of application due to its versatility and biocompatibility, is predicted to be achievable by using evolutionary technique, based on first-principles calculations. Herein, the candidate structure of HfO2 is revealed to adopt a tetragonal structure under high-pressure phase with P4/nmm space group. This evidently confirms the stability of the HfO2 structures, since the decomposition into the component elements under pressure does not occur until the pressure is at least 200 GPa. Moreover, phonon calculations can confirm that the P4/nmm structure is dynamically stable. The P4/nmm structure is mainly attributed to the semiconducting property within using the Perdew-Burke-Ernzerhof, the modified Becke-Johnson exchange potential in combination with the generalized gradient approximations, and the quasi-particle GW approximation, respectively. Our calculation manifests that the P4/nmm structure is likely to be metal above 200 GPa, arising particularly from GW approximation. The remarkable results of this work provide more understanding of the high-pressure structure for designing metal-oxide-based semiconducting materials.
|
|
| 4. |
- Kotmool, Komsilp, et al.
(författare)
-
Structural Phase Transitions, Electronic Properties, and Hardness of RuB4 under High Pressure in Comparison with FeB4 and OsB4
- 2020
-
Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:27, s. 14804-14810
-
Tidskriftsartikel (refereegranskat)abstract
- We have employed an evolutionary algorithm with first-principles calculations to investigate the pressure-induced structural evolution of RuB4 up to 500 GPa. The ambient phase is predicted to be a hexagonal structure (P6(3)/mmc). The novel phases consisting of monoclinic (C2/c) and orthorhombic (Immm) structures are proposed to be the high-pressure phases at the pressure intervals of 198-388 GPa and beyond 388 GPa, respectively. The stability of the predicted phases is confirmed by both dynamic and elastic calculations. The electronic and mechanical properties of the predicted phases are evaluated and mainly discussed compared to the isoelectronic metal tetraborides, i.e., FeB4 and OsB4. In contrast to FeB4 and OsB4, all the stable phases of RuB4 are metal or semimetal, and any semiconducting phases do not emerge in the transformation pathway of RuB4. The nature of chemical bonding investigated by ELF, MPA, and pCOHP calculations reveals that the atomic configurations and the degree of covalent bonding of the predicted phases are responsible for lower hardness compared to those of FeB4 and OsB4. The results of this work provide more understanding of the family of metal tetraboride for designing metal-boride-based hard/superhard materials.
|
|
| 5. |
- Pluengphon, Prayoonsak, et al.
(författare)
-
Formation of Lightweight Ternary Polyhydrides and Their Hydrogen Storage Mechanism
- 2021
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:3, s. 1723-1730
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied Na-Li-H compositions by mixing cations of Na and Li under high pressure using ab initio random structure searching and cluster expansion techniques. We have found that high pressure induces the structural stability of Na3LiH12, Na2Li2H12, and NaLi3H12 compounds. Our phonon calculations confirm the dynamical stability of these compounds, whereas our elastic constant calculations confirm their mechanical stability. Convex hull at 25 GPa indicates the minimum of relative enthalpy in Na2Li2H12, which is the new discovery at lower pressure than other alkali-polyhydride substances. The thermodynamic stability with respect to temperature is analyzed using quasi-harmonic oscillation approximation. Furthermore, NaLiH6 exhibits a high gravimetric hydrogen capacity, which makes this material a potential hydrogen storage candidate. We have also reported the formation enthalpy of hydrogen vacancies as well as the hydrogen diffusion in this lightweight ternary polyhydride system for its practical use in energy storage application.
|
|
| 6. |
- Pluengphon, Prayoonsak, et al.
(författare)
-
Thermodynamic and dynamic stability of NaLiC4 : Exploring superconductivity in a layered hexagonal compound through first-principles calculations
- 2024
-
Ingår i: Journal of Physics and Chemistry of Solids. - : Elsevier. - 0022-3697 .- 1879-2553. ; 189
-
Tidskriftsartikel (refereegranskat)abstract
- The layered hexagonal compound NaLiC4 has been thoroughly investigated to assess its thermodynamic and dynamic stability in comparison to its parent compounds NaC2 and LiC2. Utilizing first -principles calculations and phonon analyzes, NaLiC4 has demonstrated remarkable stability within a pressure range of 10 to 100 GPa, surpassing the thermodynamic stability of NaC2 and LiC2. It exhibits metallic behavior with distinctive electronic bands along high symmetry paths, suggesting a conducive environment for superconductivity. The superconducting transition temperature (Tc) of NaLiC4 under different pressures was estimated using the Allen- Dynes equation, with a maximum Tc of 79 K observed at 10 GPa. However, as pressure increases, Tc gradually decreases, indicating the significant impact of external pressure conditions on the superconducting properties. Notably, the in-plane E2g phonon mode originating from the layered hexagonal structure of carbon atoms plays a crucial role in facilitating electron-phonon coupling and influencing the superconducting behavior and Tc of NaLiC4. These findings highlight the thermodynamic and dynamic stability of NaLiC4 as a promising candidate for exploring superconductivity, offering insights into its electronic properties, pressure -dependent Tc behavior, and the influence of specific phonon modes. Further theoretical investigations and experimental studies are necessary to fully unlock the potential of NaLiC4 and its contribution to the development of high-performance superconductors.
|
|
| 7. |
- Pluengphon, Prayoonsak, et al.
(författare)
-
TM dopant-induced H-vacancy diffusion kinetics of sodium-lithium alanates : Ab initio study for hydrogen storage improvement
- 2022
-
Ingår i: International journal of hydrogen energy. - : Elsevier. - 0360-3199 .- 1879-3487. ; 47:43, s. 18763-18771
-
Tidskriftsartikel (refereegranskat)abstract
- We present a hydrogen storage mechanism of the surface and bulk NaeLieAl hydrides substituted by the transition metal (TM) dopants such as Ni, Cu, Ag, and Zn. The host hydrides of interest, namely, NaAlH4, LiAlH4, Na3AlH4, Li3AlH4, and Na2LiAlH4 are found to be stable compositions at ambient pressure. Hydrogen vacancy mechanisms of the host hydrides with the TM dopants are investigated using ab initio calculations. Remarkably, the results show the enhancement of the internal mechanism for hydrogen storage in the Na-Li-Al complex hydrides. Doping of Ni or Zn mainly reduces the energy barrier of diffusion kinetics in the host Na-Li-Al hydrides, leading to the improvement of the hydrogen storage efficiency of the host Na-Li-Al hydrides. Therefore, hydrogen vacancy diffusion kinetics in the Na-Li-Al hydrides can be induced by adding the Ni and Zn dopants. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
|
|
| 8. |
- Sukmas, Wiwittawin, et al.
(författare)
-
First-principles calculations on superconductivity and H-diffusion kinetics in Mg-B-H phases under pressures
- 2023
-
Ingår i: International journal of hydrogen energy. - : Elsevier. - 0360-3199 .- 1879-3487. ; 48:10, s. 4006-4015
-
Tidskriftsartikel (refereegranskat)abstract
- Focusing towards ternary metal hydrides has recently been regarded as a new avenue for research in pressure-dependent high-temperature superconductors, thanks highly to a fairly large number of permutations of alloying metals, even metalloids, with hydrogen. Herein, new phases of Mg- B- H ternary hydrides are predicted from the first-principles evolutionary techniques, as a result of which the corresponding phonon and electronic calculations for the three candidate phases are performed successively to confirm their dynamic stability and the possibility to become conductors. The metallic MgBH9 undergoes a superconducting phase with a maximum Tc of 64 K at 110 GPa, with its spectral function predominantly active around optical modes. The significant increase in cumulative electron-phonon coupling constant is associated with a relatively low cutoff frequency according to the bandwidth function. As for the non-metallic candidate, hydrogen-vacancy diffusion kinetics of the MgB2H8 phase are determined by means of total energy calcula- tions. Stable pathways at varying pressure are reported, suggesting that elevated pressure lowers the activation energy which is presumably due to an optimal level of average nearest H- H(B) inter-fragment distances.
|
|
| 9. |
- Sukmas, Wiwittawin, et al.
(författare)
-
Roles of optical phonons and logarithmic profile of electron-phonon coupling integration in superconducting Sc0.5Y0.5H6 superhydride under pressures
- 2022
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 901
-
Tidskriftsartikel (refereegranskat)abstract
- The stable structure of symmetrically Sc/Y-substituted hexahydride Sc(0.5)Y(0.5)H(6 )under high pressures is theoretically reported herein to superconduct with maximum T-c of 127 K, as supported by analyses of the electronic band structure, Fermi surface topologies, phonon dispersion, and the Eliashberg spectral function. We also expatiate on an alternative approach in describing the nature of T-c under pressures, i.e. the bandwidth function as an approximation of the spectral function (alpha(2) F) for Sc0.5Y0.5H6. Being a special case, the bandwidth function is derived from an analytic solution for the alpha F-2 function given constraints arising from the characteristics of the function itself. The consistency between the DFT-obtained alpha F-2 function and that of the proposed model suggests the dominant role played by the cutoff frequency for the optical modes in affecting T-c. (C) 2021 Elsevier B.V. All rights reserved.
|
|
| 10. |
- Tsuppayakorn-aek, Prutthipong, et al.
(författare)
-
Enthalpy stabilization of superconductivity in an alloying S-P-H system : First-principles cluster expansion study under high pressure
- 2021
-
Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 190
-
Tidskriftsartikel (refereegranskat)abstract
- The metallic ternary compound phase of S-P-H material is predicted to be the ground-state structure by first principles cluster expansion. We find that the S0.75P0.25H3, S0.5P0.5H3, and S0.25P0.75H3 structures are thermodynamically stable. The characteristic of phonon dispersions shows that the S0.75P0.25H3 and S0.5P0.5H3 structures are dynamically stable at 200 GPa. The solution of the Fermi surface supports the values of superconducting transition temperature (Tc). In addition, the electron localization function and the projected crystal orbital Hamilton populations reveal that the nature of chemical bonding shows the degree of covalent bonding of the S0.75P0.25H3 and S0.5P0.5H3 structures, supporting the Tc value. Our results show that the S0.5P0.5H3 structure is the highest Tc among the S-P-H system. The Tc of the S0.5P0.5H3 structure is estimated to be 89 K at 200 GPa.
|
|
