Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Size effect on melting of ternary CuTiZr nanoparticles : a molecular dynamics study
Serap Senturk Dalgic 1 * and Oguz Gulseren 2
1 Departmen of Physics, Trakya University, Edirne, 22030, Turkey
2 Department of Physics, Bilkent University, Ankara, 06800, Turkey
Abstract-In the present study, the melting process of spherical CuTiZr ternary nanoparticles with the diameters around 3–9nm has been
simulated by the tight binding second moment approximation (TB-SMA) model potential. Size depending melting properties of CuTiZr
nanop articles are investigated with the composition Cu 50 Ti 25 Zr 25 . We find that the melting temperatures of CuTiZr nanoparticles are lower
than that of the bulk. The size dependent melting temperature, surface energy and cohesive energy for corresponding ternary nanop articles
have been predicted.
The melting of nanomaterials is under considerable
investigation because of the broad scientific and
technological interest for possible applications. It is
important and necessary to understand and predict the
thermodynamics of nanomaterials for fabricating the
materials for practical applications.
In recent years, the ternary Cu-Ti-Zr system has attracted
increasing interest because of its good glass forming ability
[1]. Even though many atomistic simulation studies have
been performed in order to investigate the atomic scale
materials phenomena of bulk metallic glassy alloys [2],
such as CuTiZr [3, 4], none has been done for nanoscale of
this material. This is mostly because of the difficulty in
developing the interatomic potentials for ternary systems
which can be used successfully in molecular dynamics
(MD) calculations.
The objective of the present work is to determine the size
dependent melting properties of ternary spherical
nanoparticles CuTiZr for the selected alloy composition.
For this purpose, we have studied the melting evolution of
Cu 50 Ti 25 Zr 25 nanoparticles using molecular dynamics
without the periodic boundary conditions. The temperature
is controlled by Nose-Hoover thermostat. Newtonian
equations of motion are integrated using the Leapfrog
Verlet method with a time step 2 fs. For bulk and
nanoparticles, system was subjected to heating process
consisting of a series of MD simulations with temperature
increments T=50 °K and relaxing time 50 ps. However,
for a temperature near the melting region, we used smaller
temperature increment, T=10 °K while keeping the
relaxation time as 50 ps.
calculations with the TB-SMA many body potential [5].
The potential parameters can deal with all the different
elements, Cu, Ti, Zr proposed by Cleri and Rosato and
alloys systems composed of those elements using common
mathematical formalism developed in Ref. [4].
In order to validate the TB potential, we first simulate the
melting process of bulk Cu 50Ti 25 Zr 25 alloys and check our
results with those presented in the literatures. The
simulation method was as follows: first of all, all spherical
nanoparticles started with geometries constructed from a
large cubic FCC crystal structure using a series of spherical
cutoff centered at a core of cubes. The stable structure at 0
K is obtained through the initial configurations annealed
fully at T=300 °K and then cooled to T=0 °K at a cooling
rate 1 K/ps. In order to get an energy-optimized structure
during heating at a given temperature for bulk systems,
molecular dynamics under constant temperature and
constant pressure conditions (NPT) with periodic boundary
conditions has been performed. For the nanoparticles, we
used the constant volume and constant temperature (NVT)
molecular
dynamics
Cu 50 Ti 25 Zr 25 . The structural properties of nanoparticles
were also studied via radial distribution function, mean
atomic distances and coordination number. The size
dependence diffusion have been established, the diffusion
mechanism for ternary nanoparticles is dominated at
surface diffusion. Surface energies for different
nanoparticles have also been calculated. In summary, the
presented study has been established to describe the size
dependences of melting properties of ternary
nanoparticles. The presented results will be verified by the
experimental and other theoretical models developed for
ternary nanoparticles in future studies.
*Corresponding author: dserap@yahoo.com
T=0 °K T =700 °K T=1100 °K
Figure 1. Snapshot views of the MD sample with N=32085
(D=9nm) at a series of temperatures during heating.
It is established experimentally that the melting begins
preferentially at the surface in the melting process of
nanoparticles and nanorods [6-8]. It has been shown in
Figure 1 that the surface atoms much more active than the
other atoms. The relations between the mean atomic
energy and temperature for different size of nanoparticles
and bulk have been obtained. The melting temperatures of
ternary Cu50Ti25Zr25 nanoparticles show clear
dependence of particle diameters. The heat of melting for
the nanoparticles is lower than that of the bulk
[1] S. Pauly, J. Das, N. Mattern, D.H. Kim, J. Eckert,
Intermetallics, 17, 453 (2009).
[2] A. Inoue, W. Zhang, T. Zhang, K. Kurosaka, Acta. Mater. 49,
2645 (2001).
[3] X. J. Han and H. Teichler Physical Review E 75, 061501
(2007)
[4] S. S. Dalgic and M. Celtek (unpublished results).
[5] F. Cleri and V. Rosato Phys. Rev. B48, 22 (1993).
[6] O Gulseren, F. Ercolessi ve E. Tosatti ; Phys. Rev B51,7377
(1995).
[7] Z.L. Wang et al. Phys. Rev. B 67, 193403 (2003).
[8] W. Hu, S. Xiao, J. Yang and Z. Zhang, Eur. Phys. J. B 45,
547 (2005).
6th Nanoscience and Nanotechnology Conference, zmir, 2010 344