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    Elastic properties of A2Ti6O13 ( A = H, Li, Na, K and Rb): a computational study
    (2023-09-21)
    Simalaotao, Kodchakorn
    ;
    Thanasarnsurapong, Thanasee
    ;
    Maluangnont, Tosapol
    ;
    Phacheerak, Kanoknan
    ;
    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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    Pressure Dependence of Structural and Elastic Properties of Na2O: First-Principles Calculations
    (2022-01-01)
    Phacheerak, Kanoknan
    ;
    Thanomngam, Pitiporn
    The effect of high pressures, up to 40 GPa, on the structural and elastic properties of sodium oxide in cubic structure (c-Na<inf>2</inf>O) were investigated by first-principles calculations. The generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functional was employed in the calculations. The calculated structural and elastic properties at zero pressure are consistent with the available results. The pressure dependence of structural and elastic properties was presented and discussed in detail. Under pressure, the elastic constants satisfy the Born criteria, indicating that c-Na<inf>2</inf>O is mechanically stable. Moreover, other elastic properties such as bulk modulus (B), shear modulus (G), and Young's modulus (E) under pressures were analyzed. Furthermore, the B/G values tend to increase with the increasing pressure, which means that pressure can improve the ductility of c-Na<inf>2</inf>O.