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Elastic properties of A2Ti6O13 ( A = H, Li, Na, K and Rb): a computational study
(2023-09-21)
Simalaotao, Kodchakorn
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Thanasarnsurapong, Thanasee
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Maluangnont, Tosapol
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Phacheerak, Kanoknan
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Boonchun, Adisak
The elastic properties of the alkali hexatitanate family A <inf>2</inf>Ti<inf>6</inf>O<inf>13</inf> (A = H, Li, Na, K, and Rb) are investigated based on density functional theory within a generalized gradient approximation plus Hubbard U (GGA+U) approach. The results showed that all members of the family are wide-band semiconductors and the calculated lattice parameters are consistent with experimental values. In terms of mechanical stability, the results indicated that the alkali hexatitanates are highly incompressible to uniaxial stress, with the largest elastic constant C<inf>22</inf> reaching values as high as 265 GPa in K<inf>2</inf>Ti<inf>6</inf>O<inf>13</inf>. The obtained elastic constants, using the stress-strain method, were used to calculate bulk modulus, shear modulus, Young’s modulus, brittleness and ductility, elastic anisotropy, Vickers hardness, sound velocities, and the Debye temperature. It was found that the member of the family with the highest atomic number of the alkaline group, Rb<inf>2</inf>Ti<inf>6</inf>O<inf>13</inf>, had the highest values of bulk, shear, and Young’s modulus, as well as the lowest values of shear and compression anisotropy, and a high Vickers hardness.
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Alternating current properties of bulk- and nanosheet-graphitic carbon nitride compacts at elevated temperatures
(2023-08-23)
Maluangnont, Tosapol
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Pulphol, Phieraya
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Chaithaweep, Kanokwan
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Dabsamut, Klichchupong
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Kobkeatthawin, Thawanrat
The investigations of temperature-dependent electrical properties in graphitic carbon nitride (g-C<inf>3</inf>N<inf>4</inf>) have been largely performed at/below room temperature on devices commonly fabricated by vacuum techniques, leaving the gap to further explore its behaviors at high-temperature. We reported herein the temperature dependence (400 → 35 °C) of alternating current (AC) electrical properties in bulk- and nanosheet-g-C<inf>3</inf>N<inf>4</inf> compacts simply prepared by pelletizing the powder. The bulk sample was synthesized via the direct heating of urea, and the subsequent HNO<inf>3</inf>-assisted thermal exfoliation yielded the nanosheet counterpart. Their thermal stability was confirmed by variable-temperature X-ray diffraction, demonstrating reversible interlayer expansion/contraction upon heating/cooling with the thermal expansion coefficient of 2.2 × 10−5-3.1 × 10−5 K−1. It is found that bulk- and nanosheet-g-C<inf>3</inf>N<inf>4</inf> were highly insulating (resistivity ρ ∼ 108 Ω cm unchanged with temperature), resembling layered van der Waals materials such as graphite fluoride but unlike electronically insulating oxides. Likewise, the dielectric permittivity ϵ′, loss tangent tan δ, refractive index n, dielectric heating coefficient J, and attenuation coefficient α, were weakly temperature- and frequency-dependent (103-105 Hz). The experimentally determined ϵ′ of bulk-g-C<inf>3</inf>N<inf>4</inf> was reasonably close to the in-plane static dielectric permittivity (8 vs. 5.1) deduced from first-principles calculation, consistent with the anisotropic structure. The nanosheet-g-C<inf>3</inf>N<inf>4</inf> exhibited a higher ϵ′ ∼ 15 while keeping similar tan δ (∼0.09) compared to the bulk counterpart, demonstrating its potential as a highly insulating, stable dielectrics at elevated temperatures.
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Enabling enhanced lithium storage capacity of two-dimensional pentagonal BN2 by aluminum doping
(2023-04-21)
Thanasarnsurapong, Thanasee
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Detrattanawichai, Panyalak
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Dabsamut, Klichchupong
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Simalaotao, Kodchakorn
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Maluangnont, Tosapol
Researchers studying Li-ion batteries (LIBs) have become very interested in two-dimensional (2D) materials possessing an unusual pentagonal atomic structure. Recently, penta-graphene, penta-B<inf>2</inf>C, and penta-BN<inf>2</inf> have been theoretically described. These materials are attractive for use as state-of-the-art anodes in LIBs due to their high storage capacities of 1489, 1594, and 2071 mA h g−1, respectively. Here, we propose enhancing storage capacity by introducing defect doping. For example, one Al atom was incorporated into 2 × 2 penta-BN<inf>2</inf>, corresponding to AlB<inf>7</inf>N<inf>16</inf>. The energy calculated for the adsorption of a single Li atom onto the Al-doped material is more favorable than that for the Al-free analog, indicating that doping can strengthen an affinity for Li. The Al-doped penta-BN<inf>2</inf> exhibits metallic conductivity during Li adsorption. In the layer-by-layer Li adsorption, doping a single Al atom into 2 × 2 penta-BN<inf>2</inf> has an 11% higher storage capacity (2297 mA h g−1) than penta-BN<inf>2</inf> despite having a slightly heavier formula weight. The Al-doped penta-BN<inf>2</inf> displays a low open-circuit voltage of 0.48 V. Substituting aluminum for boron enhances the Li adsorption capacity of penta-BN<inf>2</inf>, and the computed storage capacity is presently one of the highest published values for pentagonal materials.
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Theoretically proposed stable polymorph of two-dimensional pentagonal β-PdPSe
(2023-01-04)
Dabsamut, Klichchupong
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Chatratin, Intuon
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Thanasarnsurapong, Thanasee
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Maluangnont, Tosapol
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Boonchun, Adisak
The theoretical discovery of new and stable 2D penta materials based on first-principles calculations has stimulated technological advances due to the anticipated exotic properties of such structures, which include the α and β phases of penta-NiPS. Inspired by the similarity between the theoretically proposed penta-NiPS and the experimentally synthesized (α phase) of penta-PdPSe, we propose herein the β phase of penta-PdPSe as a new penta-2D material. Comprehensive analyses indicated that β phase penta-PdPSe is thermodynamically, dynamically, mechanically, and thermally stable, similar to its NiPS analogue. It was found that β penta-PdPSe is a wide band gap semiconductor with an indirect band gap of 1.58 eV, significantly lower than 2.15 eV for the α phase. Moreover, the two polymorphs of penta-PdPSe are soft materials with 2D Young's modului of E<inf>a</inf> = 151 N m−1 and E<inf>b</inf> = 123 N m−1 for the β phase, compared with E<inf>a</inf> = 155 N m−1 and E<inf>b</inf> = 113 N m−1 for the α phase. The calculated absorption coefficient showed that β phase penta-PdPSe is acceptable for electronic and optical nanodevices.
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Two-Dimensional Penta-NiPS Sheets: Two Stable Polymorphs
(2022-11-17)
Dabsamut, Klichchupong
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Thanasarnsurapong, Thanasee
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Chatratin, Intuon
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Maluangnont, Tosapol
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Jungthawan, Sirichok
The discovery of new and stable two-dimensional (2D) materials with exotic properties is essential for technological advancement. Inspired by the recently reported penta-PdPSe, we proposed penta-NiPS as a new member of the penta-2D materials based on first-principles calculations. The penta-NiPS monolayer is stable in two polymorphs including the α phase with an identical structure as penta-PdPSe and the newly proposed β phase with rotated sublayers. Comprehensive analyses indicated that both phases are thermodynamically, dynamically, mechanically, and thermally stable. The penta-NiPS is a soft material with 2D Young's modulus of E<inf>a</inf>= 208 N m-1and E<inf>b</inf>= 178 N m-1for the α phase and E<inf>a</inf>= 184 N m-1and E<inf>b</inf>= 140 N m-1for the β phase. Interestingly, the α-penta-NiPS showed nearly zero Poisson's ratios along the in-plane direction, where its dimensions would be maintained when being extended. For electronic application, we demonstrated that penta-NiPS is a wide band gap semiconductor with an indirect band gap of 2.35 eV for the α phase and 2.20 eV for the β phase.
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Electric field- and strain-induced bandgap modulation in bilayer C2N
(2022-05-16)
Dabsamut, Klichchupong
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Maluangnont, Tosapol
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Reunchan, Pakpoom
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T-Thienprasert, Jiraroj
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Jungthawan, Sirichok
Recently, the C2N monolayer with an optical bandgap of 1.96 eV has emerged as a novel two-dimensional material for modern optoelectronic devices. Herein, we report its bandgap modulation by using a simple bilayer formation that includes the application of an electric field and strain. We identify four energetically favorable bilayer configurations (AA-, AB-, AB′-, and Min-stacking) by using a hybrid functional, obtaining a calculated bandgap of 1.3-1.6 eV. When subjected to a perpendicular electric field up to 4 V/nm, the bandgap decreases by as much as 0.5 eV, which correlates with the increasing energy of the valence-band maximum, where the N-px and N-py states shift closer to the N-pz state. Without the electric field, the bandgap decreases when the interlayer distance is contracted by a compressive strain. We express the strain (or interlayer distance) and the physical applied pressure via the stabilized jellium equation of state. For the Min-stacking configuration, the bandgap decreases from 1.75 to 0.9 eV upon applying a pressure of 35 GPa. The strain-induced reduction in the bandgap is similarly monitored under an applied electric field. Our theoretical work suggests that the electric field and strain (or applied pressure) can be used to tune the electronic properties of the bilayer C2N.
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Towards a new packing pattern of Li adsorption in two-dimensional pentagonal BCN
(2022-04-29)
Ananchuensook, Aroon
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Dabsamut, Klichchupong
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Thanasarnsurapong, Thanasee
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Maluangnont, Tosapol
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T-Thienprasert, Jiraroj
Two-dimensional (2D) materials with a penta-atomic-configuration, such as penta-graphene and penta-B<inf>2</inf>C, have received great attention as anodes in Li-ion batteries (LIBs). Recently, penta-BCN has been demonstrated to exhibit the highest theoretical capacity to date of 2183 mA h g−1, corresponding to the composition Li<inf>3</inf>BCN. Herein, we study the layer-by-layer Li adsorption on penta-BCN by explicitly and comprehensively considering its structure. We discover a new, more energetically favorable Li adsorption site that is distinct from the latest report by Chen et al. (Phys. Chem. Chem. Phys., 2021, 23, 17693). The possible migration pathway and the accompanying activation energy are also investigated. Full lithium adsorption leads to the formula Li<inf>2</inf>BCN and the reduced theoretical capacity of 1455 mA h g−1. Still, penta-BCN exhibits metallic conductivity during Li adsorption, and has a low open-circuit voltage, and a low ion-diffusion barrier, all being beneficial for anode materials. These observations imply that penta-BCN remains one of the most effective anode materials for LIBs with a quick charge/discharge rate.
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Direct conversion of carboxylic acid to olefins over Pt-loaded, oxygen-deficient alkali hexatitanate catalysts with ketonization-hydrogenation-dehydration activity
(2021-09-01)
Promchana, Pratya
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Boonchun, Adisak
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T-Thienprasert, Jiraroj
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Sooknoi, Tawan
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Maluangnont, Tosapol
The production of long chain olefins from fatty acids via decarbonylation is limited by low olefins selectivity at high conversion. Here, we reported the direct acid-to-olefins conversion via the ketonization-hydrogenation-dehydration sequence at 400 °C and atmospheric 10 %H<inf>2</inf>/Ar. The oxygen vacancy defects (V<inf>O</inf>) were essential in acetic acid ketonization over the oxygen-deficient alkali hexatitanate A<inf>2</inf>Ti<inf>6</inf>O<inf>13-</inf><inf>x</inf> (A[dbnd]K, Na and Li) catalysts, as evidenced from the activity of reduced vs non-reduced catalysts. The presence of V<inf>O</inf> was deduced spectroscopically with XPS and DRUV-VIS, and the ease of V<inf>O</inf> formation was ranked via the DFT calculations. The ketonization activity was proportionated to the square of the V<inf>O</inf> content (x2), consistent with the bimolecular reaction mechanism. The Pt-loaded K<inf>2</inf>Ti<inf>6</inf>O<inf>13-</inf><inf>x</inf> enabled the direct acid-to-olefins transformation as shown by a complete conversion of two model compounds (heptanoic acid and lauric acid) with ∼30–40 % yield of long chain olefins. Heptanoic acid (C<inf>7</inf>) underwent ketonization to 7-tridecanone (a C<inf>13</inf> ketone) prior to the hydrogenation-dehydration to 7-tridecene, a C<inf>13</inf> olefin. The strong metal-support interaction (SMSI) between Pt and K<inf>2</inf>Ti<inf>6</inf>O<inf>13-</inf><inf>x</inf> inhibited further hydrogenation of the olefin to a low-value alkane. For lauric acid (C<inf>12</inf>), 12-tricosene (a C<inf>23</inf> olefin) was produced analogously. The catalytic activity and products selectivity over Pt-loaded K<inf>2</inf>Ti<inf>6</inf>O<inf>13-</inf><inf>x</inf> significantly depended on the Pt content (0–1.0 wt%). The simultaneous C[sbnd]C coupling and oxygen removal prior to the subsequent hydrogenation and dehydration is a potential approach toward the production of long chain olefins with the (2n-1) carbon atoms from C<inf>n</inf>-fatty acids.
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Strain engineering and thermal conductivity of a penta-BCN monolayer: A computational study
(2021-09-01)
Dabsamut, Klichchupong
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Thanasarnsurapong, Thanasee
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Maluangnont, Tosapol
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T-Thienprasert, Jiraroj
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Jungthawan, Sirichok
Two-dimensional (2D) pentagonal nanostructures have been caught research attention down to their electronic, optical, mechanical and thermal transport properties. Among them, the newly proposed ternary penta-BCN monolayer shows a great potential for piezoelectric materials according to intrinsic piezoelectricity and spontaneous polarization. Nevertheless, the effect of strain toward these properties of the penta-BCN has not been elucidated. In this study, using density-functional theory with the Perdew-Burke-Ernzerhof (PBE) functional, we have investigated the impact of a uniform biaxial strain on the electronic structure and the thermal conductivity of the semiconducting penta-BCN single sheet. The strain-free penta-BCN monolayer is mechanically and dynamically stable with an indirect band gap of 1.70 eV. The sheet is rather soft as judged from the low in-plane Young's moduli. The pentagonal structure is preserved up to the yielding point of 18.4%, beyond this point the irreversible transition into the dynamically unstable, honeycomb-like system is observed. In contrast, the penta-BCN has dynamically instability under the compressive strain as small as -4%. The PBE band gap of the penta-BCN monolayer could be tuned within a range of 1.36-1.70 eV, falling into the infrared spectrum. The calculated lattice thermal conductivity of penta-BCN is around 97 W m-1 K-1 at temperature of 300 K, and decreases with increasing temperature.
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Piezoelectric and electronic properties of hydrogenated penta-BCN: A computational study
(2021-03-07)
Thanasarnsurapong, Thanasee
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Dabsamut, Klichchupong
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Maluangnont, Tosapol
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T-Thienprasert, Jiraroj
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Jungthawan, Sirichok
The pentagonal boron carbon nitride (penta-BCN) monolayer has been recently proposed as a new member of the pentagon-based two-dimensional nanosheets [Zhao et al., J. Phys. Chem. Lett. 11(9), 3501 (2020)]. By using density functional theory with the generalized gradient approximation, we have carried out detailed investigations of a hydrogenated penta-BCN sheet, where the pristine penta sheet is decorated with H atoms to the composition BCNH2. The hydrogenated penta-BCN (H-BCN) structure is mechanically, thermally, and dynamically stable. It has a wide and indirect bandgap of 4.46 eV, contrasting with the direct gap of 1.70 eV in pristine BCN. H-BCN is environmentally stable at 1 bar of H2 down to 10-10 bar; beyond this point, pristine BCN becomes more stable. Compared with penta-BCN, the components of the elastic modulus tensor C 11 and C 12 of hydrogenated penta-BCN are reduced, while C 12 and C 66 are increased. The strain tensors of piezoelectricity in H-BCN are d 21 = 0.462, d 22 = 0.213, and d 16 = 1.03 pm / V, which are lower than those of pristine penta-BCN. The hydrogenated BCN structure displays a higher spontaneous polarization Ps than penta-BCN (4.64 × 10-10 vs 3.38 × 10-10 C/m, respectively). The smaller in-plane Young's moduli E a and E b for H-BCN indicated that that they are softer than those for penta-BCN. Strain engineering can help tune electronic properties. In agreement with this claim, we found that the indirect gap of H-BCN was tunable from 4.46 to 3.26 eV under an applied tensile strain of 0%-16%, the range where the structure is dynamically stable throughout. Meanwhile, H-BCN is dynamically unstable under an applied compressive strain.

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