KMITL

Permanent URI for this communityhttps://dspace.kmitl.ac.th/handle/123456789/1

Browse

Search Results

Now showing 1 - 10 of 17

Some of the metrics are blocked by your
consent settings
Topology of boron substitutional defects in single-walled carbon nanotubes: A first-principles study
(2024-06-01)
Prachamon, Wutthisak
;
Jaiboon, Oruethai
;
Komin, Sittipong
;
Ruttanapun, Chesta
;
Limpijumnong, Sukit
This is a theoretical study of boron-doped single-walled carbon nanotubes. The same topology of primitive nanodomains, located at different positions on single-walled carbon nanotubes, leads to different electronic band structures. We propose a ϕ term. Density functional theory was corrected for van der Waals interactions and used to carry out the periodic boundary condition geometry optimization, where boron formed the topologies of primitive nanodomains. The calculated bulk structure and local structure spectroscopic parameters can be used for comparison with experimental results to confirm the theoretical models.
Some of the metrics are blocked by your
consent settings
A first principles investigation on the structural, elastic, and mechanical properties of MAX phase M3AlC2 (M= Ta, Ti, V) as a function of pressure
(2022-03-01)
Sailuam, Wutthigrai
;
Fongkaew, Ittipon
;
Limpijumnong, Sukit
;
Phacheerak, Kanoknan
This study investigated the structural, elastic, and mechanical properties of hexagonal M<inf>3</inf>AlC<inf>2</inf> (M = Ta, Ti, and V) within MAX phases by first-principles calculations. The considered properties of M<inf>3</inf>AlC<inf>2</inf> (M = Ta, Ti, and V) compounds at 0 GPa were in reasonable agreement with available experimental and other theoretical data. The elastic stability shows that no structural phase transition occurred in pressure up to 20 GPa for all compounds. The resistances to linear compression were more forceful than the resistances to compression in shape. The bulk modulus, shear modulus, and Young's modulus for M<inf>3</inf>AlC<inf>2</inf> (M = Ta, Ti, and V) compounds follow the order Ta<inf>3</inf>AlC<inf>2</inf> > V<inf>3</inf>AlC<inf>2</inf> > Ti<inf>3</inf>AlC<inf>2</inf>. The Bader charge analysis result shows the increasing of covalence bond in their structure after the pressure increased. Furthermore, Pugh's criterion B/G and Poisson's ratio v confirmed that the M<inf>3</inf>AlC<inf>2</inf> (M = Ta, Ti, and V) compounds had intrinsic brittleness. The sound velocity and Debye temperature of all compounds increased with pressure increasing. The bond stiffness and the shear anisotropy affected by pressure were reported and discussed.
Some of the metrics are blocked by your
consent settings
Effect of pressure on structural and elastic properties of SnSe: First-principles calculations
(2022-02-01)
Phacheerak, Kanoknan
;
Thanomngam, Pitiporn
;
Limpijumnong, Sukit
Selected structural and elastic properties of an orthorhombic SnSe at an ambient pressure and under high pressures were investigated using first-principles calculations. At ambient pressure, the calculated structural parameters and elastic constants show a good agreement with previously reported values. Effects of pressure on structural and elastic properties were presented and discussed in detail. Moreover, the pressure dependence of selected structural and elastic properties, which relate to phase transition from an orthorhombic phase to the high-pressure phase, was analyzed. We suggested that the phase transition is related to the compression along the c- and b-axis which correspond to C<inf>33</inf> and C<inf>22,</inf> respectively.
Some of the metrics are blocked by your
consent settings
The pressure effect on the structural, elastic, and mechanical properties of orthorhombic MgSiN2 from first-principles calculations
(2021-10-01)
Bootchanont, Atipong
;
Phacheerak, Kanoknan
;
Fongkaew, Ittipon
;
Limpijumnong, Sukit
;
Sailuam, Wutthigrai
Pressure effect on lattice parameters, elastic moduli, Poisson's ratio, Cauchy pressure, elastic anisotropy, and Vickers hardness of orthorhombic MgSiN<inf>2</inf> by means of first-principles calculations based on density functional theory (DFT) by generalized gradient approximation (GGA) in the functional form by Perdew, Bruke, and Ernzerhof (PBE) of the exchange-correlation were presented. The structural properties, elastic moduli, B<inf>0</inf>/G, Poisson's ratio (ν) and Cauchy pressure under pressure up to 10 GPa were calculated. The optimized structural and ground state properties under ambient pressure were in agreement with the available experiments and other calculations. The orthorhombic MgSiN<inf>2</inf> was mechanically stable under pressure up to 10 GPa by the elastic stability criteria investigation. Under pressure, the relationship of elasticity in length was C<inf>33</inf> > C<inf>11</inf> > C<inf>22</inf>, indicating that it is easier to compress along the b-axis than along the a-axis and c-axis, respectively. The calculated bulk modulus, shear modulus, Young's modulus and Poison's ratio index all increased with an increase in the pressure. The B<inf>0</inf>/G, Poisson's ratio (ν) and Cauchy pressure analyses implied that orthorhombic MgSiN<inf>2</inf> was single crystal, and a critical pressure for brittle-to-ductile transition was found to be 2 GPa. The Cauchy pressure of {100} plane, {010} plane and {001} plane, Vickers hardness (H<inf>v</inf>) and the shear anisotropy as a function of pressure were investigated from the calculation.
Some of the metrics are blocked by your
consent settings
Elastic and mechanical properties of hydroxyapatite under pressure: A first-principles investigation
(2020-09-01)
Sailuam, Wutthigrai
;
Phacheerak, Kanoknan
;
Atipong bootchanont
;
Fongkaew, Ittipon
;
Limpijumnong, Sukit
The structural, elastic, and mechanical properties of hydroxyapatite (HAp) were investigated by generalized gradient approximation (GGA) in the functional form by Perdew, Bruke, and Ernzerhof (PBE) exchange-correlation functional using density-functional theory. Our calculated equilibrium lattice parameters at ambient pressure are in good agreement with the experimental and previous theoretical results. The details of the structural, mechanical, and electrical properties such as elastic constants, bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratioν, Cauchy pressure, shear anisotropic factor A, and total density of states under pressure ranging 0 GPa to 10 GPa are studied. The lattice parameters a and c are found to be decreased with increasing pressure. Moreover, the lattice parameter a is more sensitive to external pressure than c. The calculated elastic constants of hexagonal HAp increase with increasing pressure. The elastic constants C<inf>11</inf> and C<inf>33,</inf> which represent the elasticity in length are larger than the elasticity in shape, which represent by the elastic constants C<inf>12</inf>, C<inf>13</inf>, C<inf>44</inf>, and C<inf>66</inf>. The deformation resistances along the axial direction are stronger than the deformation resistances in shape. The calculated B/G, Poisson's ratio ν, and Cauchy pressure show that the hexagonal HAp behaves as a ductility material at ambient pressure and has more ductile under pressure. While the calculated shear anisotropic factor A indicate that the HAp shows elastic anisotropy under pressure. Moreover, calculated total density of states (DOS) show that HAp becomes more insulator property with increasing pressure.
Some of the metrics are blocked by your
consent settings
First-principles investigations of structural and elastic properties of LiGaO2 under pressure
(2019-09-01)
Sailuam, Wutthigrai
;
Busayaporn, Wutthikrai
;
Limpijumnong, Sukit
;
Phacheerak, Kanoknan
The structural and elastic properties of the LiGaO<inf>2</inf> with an orthorhombic-type structure (Pna2<inf>1</inf>-LGO) under pressure were investigated using first-principles calculations. The calculated structural parameters and elastic constants show a good agreement with the experimental and other theoretical values. The structural parameters and elastic constants of Pna2<inf>1</inf>-LGO under various pressures are calculated. All structural parameters are found to be decreased with pressure. The elastic constants are found to increase with pressure, except for C<inf>44</inf> and C<inf>55</inf>. It was also found that the elastic constants C<inf>11</inf>, C<inf>22</inf>, and C<inf>33</inf> which represent the elasticity in length are always larger than the elastic constants C<inf>12</inf>, C<inf>13</inf>, C<inf>23</inf>, C<inf>44</inf>, C<inf>55</inf>, and C<inf>66</inf> which represent the elasticity in shape at the same pressure. The details of pressure dependences of the structural and elastic constants are also presented and discussed.
Some of the metrics are blocked by your
consent settings
Local structure of stoichiometric and oxygen-deficient A 2Ti6O13 (A = Li, Na, and K) studied by X-ray absorption spectroscopy and first-principles calculations
(2018-10-21)
Kanchanawarin, Jarin
;
Limphirat, Wanwisa
;
Promchana, Pratya
;
Sooknoi, Tawan
;
Maluangnont, Tosapol
Oxygen vacancy defects (V<inf>O</inf>) in Ti-based oxides play important roles in catalytic processes despite limited knowledge regarding their formation and characterization. Here, we demonstrate the use of X-ray absorption spectroscopy (XAS) measurements to compare the relative proportion of V<inf>O</inf> defects in as-grown alkali hexatitanate A<inf>2</inf>Ti<inf>6</inf>O<inf>13</inf> (A = Li, Na, K). Both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions were studied. The similarity of measured XANES spectra of Ti K-edge in all samples indicates the presence of (Ti<sup>4+</sup>)O<inf>6</inf> units in good agreement with reported X-ray diffraction results. The small influence of cations A at the tunnel was observed and can be well reproduced in the simulated spectra. In addition, we present a semi-quantitative approach to intuitively determine the content of V<inf>O</inf> defects in oxygen-deficient K<inf>2</inf>Ti<inf>6</inf>O<inf>13-x</inf> by in situ time-resolved XAS measurements under reducing conditions (10%H<inf>2</inf>/Ar, 50-650 °C). The in situ XANES measurements indicate that the oxidation state of bulk Ti remains the same as the as-grown sample, i.e., 4+, at elevated temperatures. By in situ EXAFS measurements, the relative number of V<inf>O</inf> defects is highest at a reduction temperature of ∼550 °C and slightly decreases after that. To confirm the formation of V<inf>O</inf> defects, first-principles calculations were independently carried out using a 126-atom K<inf>2</inf>Ti<inf>6</inf>O<inf>13</inf> supercell with V<inf>O</inf> at various positions. Based on calculated EXAFS, the removal of the oxygen atom nearest to the tunnel, which is the lowest energy structure, provides a good match to the experimental spectra.
Some of the metrics are blocked by your
consent settings
Pressure-induced phase transformations of LiGaO2: First principles study
(2017-08-01)
Sailuam, Wutthigrai
;
Sarasamak, Kanoknan
;
Polanco, Miguel Angel Mendez
;
Limpijumnong, Sukit
Phase transformations of β-LiGaO<inf>2</inf> (Pna2<inf>1</inf>) under different pressure conditions are studied using first principles calculations. Under specific conditions, LGO can exist in various structures some of which have not been previously reported (oP16 and P4<inf>1</inf>2<inf>1</inf>2). Under sufficiently strong hydrostatic pressure, LGO can transform into a rocksalt-like structure. Under strong uniaxial stress LGO can transform into a tetragonal structure or an orthorhombic structure depending on the orientation of the applied stress. The stability of different crystal structures under different applied stresses and the phase transformation processes are studied by calculating the enthalpy surfaces and transformation barriers under different stresses.
Some of the metrics are blocked by your
consent settings
First Principles Calculations of Structural and Elastic Properties of Perovskite Crystals: The Case of SrTiO3
(2016-06-01)
Pandech, Narasak
;
Sarasamak, Kanoknan
;
Limpijumnong, Sukit
The structural and elastic properties of perovskite crystals can be independently calculated by using first principles calculations without bias. The detailed calculation of cubic perovskite (Pm3m) crystal by first-principles calculations both LDA and GGA approaches was shown, using SrTiO<inf>3</inf> as an illustration case. The equilibrium volumes and bulk modulus of SrTiO<inf>3</inf> were evaluated by fitting to Birch-Murnaghan equation of states. The C<inf>11</inf>, C<inf>12</inf>, and C<inf>44</inf> elastic constants were obtained from a polynomial fit to the calculated energy-strain relations. For SrTiO<inf>3</inf>, the calculated lattice constants, bulk modulus, and all three elastic constants by both LDA and GGA calculations are in good agreement with experimental values. Because LDA gives a slightly smaller lattice constant compared to that obtained from GGA, the bulk modulus and all three elastic constants obtained from LDA are slightly larger than those values obtained from GGA. The calculation steps illustrated here can be used as a guideline to study elastic properties of other novel materials.
Some of the metrics are blocked by your
consent settings
First-principles study of Bi and Al in orthorhombic PbZrO3
(2016-04-01)
Chotsawat, Maneerat
;
Sarasamak, Kanoknan
;
Thanomngam, Pitiporn
;
Limpijumnong, Sukit
;
T-Thienprasert, Jiraroj
Lead zirconate PbZrO<inf>3</inf> (PZO) is one of the most important ceramic materials due to its antiferroelectric property, which can be used in many technological applications. Due to the toxicity of Pb, there is an attempt to replace Pb with other non-toxic elements. It has been reported that doping orthorhombic-PZO with Bi and Al atoms could stabilize the antiferroelectric property in a wide temperature range and reduce the lead content in the material. In this work, we used first-principles calculations based on density functional theory to investigate the microscopic and electronic structures of Bi and Al defects in orthorhombic-PZO. Our calculated defect formation energies revealed that Bi atom can substitute on either Pb site (A-site) or Zr site (B-site); depending on the Fermi-level as well as the crystal growth condition. On the other hand, Al atom is likely to substitute only on the Zr site. In addition, our calculations revealed that there is only a small binding between Bi<inf>Pb</inf> and adjacent Al<inf>Zr</inf> or Bi<inf>Zr</inf> with the binding energies of ∼0.2 eV. This indicates that Bi<inf>Pb</inf> and Al<inf>Zr</inf> (or Bi<inf>Zr</inf>) are unlikely to form complexes.

KMITL

Browse

Filters

Settings

Sort By

Results per page

Search Results