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Hydrogenation-induced superconducting properties of MgB2 investigated using Migdal–Eliashberg formalism: Insights from a first-principles study
(2024-09-01)
Tsuppayakorn-aek, Prutthipong
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Sukmas, Wiwittawin
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Pluengphon, Prayoonsak
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Petchsirivej, Sukanya
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Sakulkalavek, Aparporn
Theoretical investigation of hydrogenation processes has applied to magnesium diborides under ambient conditions, which identified two structurally stable phases, i.e, Mg<inf>4</inf>B<inf>6</inf>H<inf>2</inf> and Mg<inf>4</inf>B<inf>4</inf>H<inf>4</inf>. These identifications were evaluated through assessments of their lattice dynamics stability using density functional perturbation theory. Both phases exhibit metallic behavior within their electronic band structures. Our findings showcase the significant impact of anisotropic Migdal–Eliashberg calculations, enhancing the superconducting properties within this system and resulting in a notably higher T<inf>c</inf> of 34 K. Mg<inf>4</inf>B<inf>4</inf>H<inf>4</inf> exhibits superconductivity with a T<inf>c</inf> of 17 K under atmospheric conditions, as determined by anisotropic Migdal–Eliashberg calculations. Our study underscores the wide range of structural variations achievable through the hydrogenation of MgB<inf>2</inf> and highlights the crucial importance of hydrogen atom placement within these structures. In addition, the calculation result indicates the influence of band dispersion characteristics on Fermi velocity, a factor attributed to both anharmonicity and harmonicity, which plays a pivotal role in determining the superconducting properties of these materials.
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Thermodynamic and dynamic stability of NaLiC4: Exploring superconductivity in a layered hexagonal compound through first-principles calculations
(2024-06-01)
Pluengphon, Prayoonsak
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Sukmas, Wiwittawin
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Tsuppayakorn-aek, Prutthipong
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Kotmool, Komsilp
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Sakulkalavek, Aparporn
The layered hexagonal compound NaLiC<inf>4</inf> has been thoroughly investigated to assess its thermodynamic and dynamic stability in comparison to its parent compounds NaC<inf>2</inf> and LiC<inf>2</inf>. Utilizing first-principles calculations and phonon analyzes, NaLiC<inf>4</inf> has demonstrated remarkable stability within a pressure range of 10 to 100 GPa, surpassing the thermodynamic stability of NaC<inf>2</inf> and LiC<inf>2</inf>. It exhibits metallic behavior with distinctive electronic bands along high symmetry paths, suggesting a conducive environment for superconductivity. The superconducting transition temperature (T<inf>c</inf>) of NaLiC<inf>4</inf> under different pressures was estimated using the Allen–Dynes equation, with a maximum T<inf>c</inf> of 79 K observed at 10 GPa. However, as pressure increases, T<inf>c</inf> gradually decreases, indicating the significant impact of external pressure conditions on the superconducting properties. Notably, the in-plane E<inf>2g</inf> 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 T<inf>c</inf> of NaLiC<inf>4</inf>. These findings highlight the thermodynamic and dynamic stability of NaLiC<inf>4</inf> as a promising candidate for exploring superconductivity, offering insights into its electronic properties, pressure-dependent T<inf>c</inf> behavior, and the influence of specific phonon modes. Further theoretical investigations and experimental studies are necessary to fully unlock the potential of NaLiC<inf>4</inf> and its contribution to the development of high-performance superconductors.
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Enhancing thermoelectric properties of Bi2Te3 film via CuI doping: Sputtering and solid iodination methods verified by ab initio calculation
(2024-04-01)
Khumtong, Tanakorn
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Theekhasuk, Nattharika
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Somdock, Nuttakrit
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Pluengphon, Prayoonsak
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Inceesungvorn, Burapat
We have introduced an innovative method for preparing CuI-doped Bi<inf>2</inf>Te<inf>3</inf> films for the first time, which was also validated through ab initio calculations. The chemical reaction between the Cu-Bi<inf>2</inf>Te<inf>3</inf> film and iodine was conducted using the solid iodination method at room temperature. The results from X-ray diffraction and energy-dispersive spectrometry suggest that the sputtering process, followed by the solid iodination method, holds promise for synthesizing CuI-doped Bi<inf>2</inf>Te<inf>3</inf> films. Additionally, appropriately doping Bi<inf>2</inf>Te<inf>3</inf> with CuI enhances the (00l) crystal orientation, increases carrier concentration and mobility, resulting in improved electrical conductivity. Furthermore, our calculation results align with our experimental findings. An excess of substitutional CuI dopant tends to generate secondary phases, leading to alterations in the intrinsic conductivity and a reduction in the thermoelectric properties of Bi<inf>2</inf>Te<inf>3</inf>. Leveraging the enhanced electrical transport properties achieved through CuI doping, the maximum power factor of the (CuI)<inf>0.2</inf>Bi<inf>2</inf>Te<inf>2.9</inf> film reaches approximately 2.40 × 10−3 W/mK2 at 423 K, representing a 66 % enhancement compared to that of the Bi<inf>2</inf>Te<inf>2.9</inf> film, which has a power factor of 1.44 × 10−3 W/mK2.
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Role of anharmonicity in phonon-mediated superconductivity of quasi- van der Waals layered XP2 (X = As, Sb, Bi) structures: Insight from first-principles calculations
(2023-10-10)
Tsuppayakorn-aek, Prutthipong
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Pluengphon, Prayoonsak
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Sukmas, Wiwittawin
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Sakulkalavek, Aparporn
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Inceesungvorn, Burapat
It is of utmost importance to prioritize the undertaking of investigating superconductivity, as it represents one of the most intriguing and significant phenomena in the field of condensed matter physics. Our research endeavors to shed light on the metallic state of van der Waals layered XP<inf>2</inf> (X = As, Sb, Bi) structures, which is crucial in predicting their superconducting properties. Employing a first-principle evolutionary algorithm, we predicted the structures of phosphides, including AsP<inf>2</inf>, SbP<inf>2</inf>, and BiP<inf>2</inf>, and determined their energetically stable configurations under atmospheric pressure. To investigate the potential for superconductivity in these structures, we conducted a thorough examination of relevant electronic properties. One of the crucial factors we addressed was the role of anharmonic phonon properties in determining the superconducting state in van der Waals layered structures. Our findings suggest that the introduction of anharmonicity can significantly suppress the superconducting abilities of such structures. Hence, the anharmonicity present in AsP<inf>2</inf>, SbP<inf>2</inf>, and BiP<inf>2</inf> could be held accountable for the lower observed superconducting critical temperature in these van der Waals layered structures.
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Role of Lifshitz transition stabilized carbon hexagon structure from biaxial strain: A case of sodium carbide with superconducting condition
(2023-06-15)
Tsuppayakorn-aek, Prutthipong
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Pluengphon, Prayoonsak
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Sukmas, Wiwittawin
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Sukserm, Akkarach
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Kotmool, Komsilp
We theoretically report on an investigation of sodium carbide system by means of first-principles calculations based on density functional theory. Herein, the diverse sodium–carbon structures are predicted by taking carbon-rich compositions of NaC<inf>2</inf> with a carbon hexagon structure as a starting point. Metallic phases of NaC<inf>2</inf> at a pressure of 100 GPa are predicted to be stabilized by biaxial strain, culminating in the strain-induced electronic topological transitions, also known as the Lifshitz transitions. We found that the flat band accommodates localized electrons around the Fermi level, originating from the effect of biaxial strain, which results in low-velocity electrons forming up to at least 20% of Cooper pairs. According to the respective phonon-mediated superconductivity, NaC<inf>2</inf> is dynamically stable not only without the influence of biaxial strain but also with that of the biaxial tensile strain, indicating possible enhancement of the critical temperature superconductor (T<inf>c</inf>). Furthermore, the estimated T<inf>c</inf> reaches 29.5 K, slightly higher than 24.7 K for the case without biaxial strain. These findings suggest that the possibility of superconductivity is promoted by the applied biaxial tensile strain. Our findings pave the way for future investigation of high superconductivity in carbon-based materials and suggest the possibility of metal-carbides being synthesisable and exhibiting quite a high T<inf>c</inf> superconductivity.
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Structural, optical, and electrical properties via two simple routes for the synthesis of multi-phase potassium antimony oxide thin films
(2022-07-15)
Homcheunjit, Ratchaneekorn
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Pluengphon, Prayoonsak
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Tubtimtae, Auttasit
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Teesetsopon, Pichanan
Multi-phase ternary oxide glass thin films of potassium antimony oxide were synthesized via dip coating (DC) and spray pyrolysis (SP) methods. The growth of thin film was conducted on a non-conductive borosilicate glass substrate. Surface morphology was investigated and showed different characteristics. X-ray diffraction (XRD) analysis revealed the peaks corresponded to the monoclinic KSb<inf>3</inf>O<inf>5</inf> and K<inf>2</inf>Sb<inf>4</inf>O<inf>11</inf> phases. The structural parameter analysis shows that the lower values of micro strain (ε), dislocation density (δ), and stacking fault probability (SF) with higher number (N) of particle in the multi-phase thin film for the spray pyrolysis method confirm slightly larger crystallite size, less crystal imperfection, and less structural disorder. The lower average transmission, absorption, and extinction coefficients resulted to higher refractive index, permittivity, and electrical susceptibility for the sample synthesized by a spray pyrolysis method. In addition, the average energy band gap values (E<inf>g</inf>) of 3.57 and 3.60 eV were obtained for the dip coating and spray pyrolysis methods, respectively. However, the lower R<inf>s</inf> (14.69 × 107 Ω/sq.) with higher σ<inf>h</inf> (85.09 S/cm) and the FOM<inf>(H-HR)</inf> (0.183 Ω-1) of the multi-phase K–Sb–O thin film for the dip coating method were obtained may be due to more interconnections generated at the interface and there are less residual on the surface of thin film.
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Improving the photo-thermoelectric performance of CuAlO2 via doping with Bi
(2021-12-01)
Daichakomphu, Noppanut
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Klongratog, Bhanupol
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Rodpun, Phumin
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Pluengphon, Prayoonsak
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Harnwunggmoung, Adul
The photothermoelectric (PTE) effect enables the conversion of temperature differences induced by absorbed light to electrical voltages. For the first time, we investigated the effect of Bi doping on the photothermoelectric properties of CuAlO<inf>2</inf>. In this study, delafossite CuAl<inf>1-x</inf>Bi<inf>x</inf>O<inf>2</inf> (x = 0.01, 0.02, 0.03, 0.04, and 0.06) powders were synthesised. X-ray diffraction and X-ray absorption spectroscopy results indicated that the doping limit of Bi content was approximately 2.6–2.7 at% (x = 0.026–0.027). At x = 0.02, we successfully demonstrated the increase of electrical conductivity due to the reduced effective mass and the increased hole concentration, the increase of optical absorption due to the reduced band gaps, and lower thermal conductivity resulting from mass and strain fluctuations. At a Bi content of 2 at%, the photovoltage signals increased compared with the undoped CuAlO<inf>2</inf>. These results indicated that Bi doping could potentially improve the PTE properties of CuAlO<inf>2</inf>.
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Nature of electronic topological transition and superconductivity in bismuth under high pressure from ab initio random structure searching
(2021-12-01)
Chaimayo, Wanaruk
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Tsuppayakorn-aek, Prutthipong
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Pluengphon, Prayoonsak
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Kotmool, Komsilp
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Pakornchote, Teerachote
We have predicted the hexagonal close-packed (hcp) structure of bismuth (Bi) using ab initio random structure searching (AIRSS) at extreme conditions. The calculation, which included spin–orbit coupling, shows that the hcp structure is thermodynamically and dynamically stable at high pressure. The electronic band structure calculations suggest the downshifting of the flat band through compression due to Lifshitz transitions. The Fermi surface shape of hcp Bi produces the metallicity in this material. The electron localization function reveals a weak bonding of Bi. The solutions of electronic topological transition and a soft-mode of phonon dispersion provide the possibility for prediction and reduction of the superconducting transition temperature.
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Improving the thermoelectric properties of thick Sb2Te3 film via Cu doping and annealing deposited by DC magnetron sputtering using a mosaic target
(2021-11-01)
Theekhasuk, Nattharika
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Sakdanuphab, Rachsak
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Nuthongkum, Pilaipon
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Pluengphon, Prayoonsak
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Harnwunggmoung, Adul
Thick Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films were deposited on flexible substrate by DC magnetron sputtering from a mosaic Cu–Sb<inf>2</inf>Te<inf>3</inf> target. The Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films were vacuum annealed to improve their thermoelectric properties. Density functional theory was used to clarify the internal mechanism of the Cu doped into the Sb<inf>2</inf>Te<inf>3</inf> system. The results showed that Cu substitution on a Sb site induced electronic states or impurity peaks of Sb<inf>2</inf>Te<inf>3</inf> at a valence band maximum. The carrier concentration of the Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films increased as the Cu-doped concentration increased. However, the crystallite size and Seebeck coefficient of the Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films decreased as the Cu-doped concentration increased. Post-annealing treatment improved the microstructure and thermoelectric properties of the Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films. The maximum electrical conductivity and power factor values of 754.20 S/cm at 50 °C and 1.56 10−3 W/mK2 at 100 °C were obtained in the annealed film with a Cu-doped concentration of 3 at%.
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Fe-doped effects on phase transition and electronic structure of CeO2 under compressed conditions from ab initio calculations
(2021-10-01)
Sathupun, Karnchana
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Kotmool, Komsilp
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Tsuppayakorn-aek, Prutthipong
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Pluengphon, Prayoonsak
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Majumdar, Arnab
Ab initio study of high-pressure phase transition and electronic structure of Fe-doped CeO<inf>2</inf> with Fe concentrations of 3.125, 6.25, and 12.5 at% has been reported. At a constant-pressure consideration, the lattice constants and the volume of the supercell were decreased with an increasing concentration of Fe. The average bond length of Fe–O is lower than that of Ce–O. As a result, Fe doping induces the reduced volume of the cell, which is in good agreement with previous experiments. At high pressure (~ 30 GPa), it was found that the transition pressure from the fluorite to the cotunnite orthorhombic phase decreases at a higher concentration of Fe, indicating that the formation energy of the compound is induced by Fe-doping. Furthermore, compression leads to interesting electronic properties too. Under higher pressures, the bandgap increases in the cubic structure under compression and then suddenly plummets after the transition to the orthorhombic phase. The 3d states of Fe mainly induced the impurity states in the bandgap. In both the undoped and Fe-doped systems, the bandgap increased in the cubic phase at high pressure, while the gap and p-d hybridization decrease in the orthorhombic phase.

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