Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
The investigation of structural, electronic and mechanical prope rties of LiPt 3 B: first-principles study
Sezgin A 1 * 1
1 Department of Physics, Gazi University, Teknikokullar, 06500, Ankara, TURKEY
Abstract- The structural, electronic and mechanical properties of LiPt 3 B compound have been investigated by using first-principles within
plane-wave density functional theory. The behaviors of the structural parameters under pressure are studied. It is shown from calculated
density of states, partial density of states and band structure that this compound exhibits metallic character. By means of calculated elastic
constants, mechanical stability of LiPt 3 B is investigated. However, micro-hardness of the compound is calculated by using the parameters
obtained from first-principles.
Since the discovery of superconductivity in MgB 2 [1],
searching new superconducting materials composed of light
elements and transition metals have attracted considerable
interest [2]. In this context, it was found that some lithium
ternary borides such as LiBC [3,4], Li 2 Pt 3 B [5,6], Li 2 Pd 3 B
[5,6] are superconductor. Therefore, in this study, the
structural, electronic and mechanical properties of LiPt 3 B
were investigated.
Crystal structure of LiPt 3B is shown in Fig.1(a) and (b) [7].
There are three boron, three lithium and nine platinum atoms
in the unit cell. Space group is P-62m (No:189). As a special
interest, the unit cell consists of lithiu m atoms and Pt 6 B
triangular prisms (see Fig1.b).
Figure 1. (a) Crystal structure of LiPt 3 B and (b) its Pt 6 B sub-unit.
Pink, purple and blue spheres stand for boron, lithium and platinum
atoms, respectively.
By mean of first-principle calculation within density functional
theory, lattice parameters, band structure and elastic constants were
calculated. It was found that a=9.284Å and c=2.784Å, and these
values are in good agreement in the Ref.[7]. Calculated band
structure were plotted in Fig.2 and from this figure, LiPt 3 B
has a metallic character.
Table 1. Calculated single crystal elastic constants in GPa unit and
mechanical properties such as bulk modulus, shear modulus, Young
modulus and Poisson ratio. V and R subscript stand for Voigt and
Reuss.
c 286.385
11
c 410.897
33
c 35.629
44
c 146.741
12
c 120.366
13
c 69.822
66
B 195.401
V
B 192.634
R
G 67.962
V
G R 53.968
G (GPa) 60.965
B (GPa) 194.018
E (GPa) 125.016
v 0.158
It is shown that due to calculated elastic constants of
LiPt 3 B satisfy mechanical stability conditions, it is
mechanically stable.
Furthermore, microhardness of LiPt 3B was calculated by
using Simunek’s method [8,9].and was found as 15.74 GPa.
Individual bond hardnesses were tabulated in Table 2. From
Table 2, strengths of Pt-B bonds are higher than that of Pt-
Pt bonds. Other word, hybridization between Pt and B
atoms are stronger than that of between Pt and Pt atoms,
and as a result of this tendency, Pt-B bonds are more
dominant than Pt-Pt bonds on the mechanical properties.
Table 2. Individual bond strengths and total hardness for LiPt 3 B.
Zi Zj Ri Rj ni nj dij ei ej Sij Bond H
10 3 1.387 0.98 2 6 2.148 7.210 3.061 0.182 Pt-B 15.74
10 10 1.387 1.387 10 9 2.805 7.210 7.210 0.029 Pt-Pt
In conclusion, LiPt 3 B has metallic character. It is
mechanically stable, but it is not a superhard material. Pt-B
bonds are stronger than Pt-Pt bonds.
This work is supported by the State of Planning
Organization of Turkey under Grant No. 2001K120590.
*Corresponding author: sezginaydin@gazi.edu.tr
Figure 2. Calculated band structure along high symmetry
directions in the first Brillouin zone for LiPt 3 B.
Calculated single crystal elastic constants were listed in
Table I with other mechanical properties.
[1] J. Nagamatsu, N. Nakagawa, T.Muranaka, Y. Zenitani, J.
Akimitsu, Nature 410, 63–64 (2001)
[2] Physica C 460–462, 89–90 (2007)
[3] H. Rosner, A. Kitaigorodsky, and W. E. Pickett,
Phys.Rev.Lett. 88, 127001 (2003)
[4] Z.Liu, X.Chen, Y.Wang, Physica B 381, 139-143 (2006)
[5] U. Eibenstein and W.Jung, Journal Of Solid State Chemistry
133, 21-24 (1997)
[6] H. Takeya et al., Physica C 445–448, 484–487 (2006)
[7] R.Mirgel, J.Wung, J.Less-Common Met.144, 87-99 (1988)
[8] A.simunek, J.Vackar, Phys.Rev.Lett. 96, 085501 (2006)
[9] A.Simunek, Phys.Rev.B 75, 172108 (2007)
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