Disordered Solids
Bulk Metallic
Glass Boron
Carbide
High-Pressure
Silica
Meso-porous Structures
Solid-state Electrolytes
We are interested in employing
Density Functional Theory (DFT), classical & ab-initio molecular dynamics
simulations and hybrid reverse Monte Carlo methods to assess the
internal characteristics of a wide range of disordered solids. The overarching
goal is to enable a better understanding of the correlation between these
characteristics and their physical properties. Below are examples of our recent
works:
We are working
closely with our collaborators at UMKC and Ohio State in developing
structural models of amorphous B4C thin film produced from gaseous
precursors e.g. B2H6, BCl3 and CH4.
We seek to identify the characteristic short-range and medium-range
orders that are present within the amorphous structures as a function of
, among others, the compositional variations of these precursors and
deposition parameters. The project has been supported by NSF through
the (Designing Materials to Revolutionize and Engineer our Future) DMREF Program.
A snapshot of MD
trajectories of the B4C amorphous structure comprised of
icosohedral clusters
S. Im, M. M. Paquette, M.
Belhadj-Larbi, P. Rulis, R. Sakidja and J. Hwang, "Nanoscale
Structure-Property Relationship in Amorphous Hydrogenated Boron Carbide
for Low-k Dielectric Applications",
Microscopy and Microanalysis, 23(S1), 1486-1487 (2017).
Bulk Metallic Glass (BMG)
An example of our more recent
work in collaboration with
Prof. W-Y Ching's group at UMKC is on the
multi-component Bulk Metallic Glass (BMG) of Vitreloy. We employed DFT
calculations and bond-order analyses to extract the critical thermo-mechanical and
electronic structure of this complex disordered solid.
Batu Hunca, Chamila Dharmawardhana, Ridwan Sakidja, and Wai-Yim Ching, "Ab
initio calculations of thermomechanical properties and electronic
structure of vitreloy Zr41.2Ti13.8Cu12.5Ni10Be22.5",
Physical Review B, 94, 144207 (2016)
Solid-state Electrolytes
Another example of our main research
interests in the disordered solids is the ab-initio
molecular dynamics (AIMD) simulation on solid-state
amorphous electrolytes. In collaboration with our colleague
Prof. Saibal Mitra from Missouri State, we are
evaluating the mobility of Li ions inside the
phosphate-based glass as a model system. We
employ ab-initio molecular dynamics (AIMD) to probe
various factors that may affect the hopping mechanisms
of Li ions inside this glass structure. Substituting
Sulfur for Phosphor for example has been shown to
enhance the Li ion mobility in the 60%(Li2O-P2O5)
40%(Li2SO4)
glass (drawn above). We
have recently shown that the substitution is also characterized by the presence of many
neighboring O
anions in the close vicinity of the Li diffusion pathway
possibly resulting in a lowered energy barrier for Li
ion to hop. Below are examples of Li ion (green)
trajectories inside the glass from AIMD simulations. Various O anions (red)
can be seen to tightly bind the Li ion throughout the
diffusion pathways. Our graduate student
Shafiq Islam
has been working on this topic for his Master's thesis
with some of the computational results
recently published in MRS Advances.
Sequential trajectories from ab-initio molecular dynamics
simulations depicting the Li hopping mechanisms
Md Shafiqul Islam, Paul Simanjuntak, Saibal Mitra
and Ridwan Sakidja, "DFT Study on the Li Mobility in Li-Ion-Based
Solid-State Electrolytes", MRS Advances, Vol. 2 [54] (Energy Storage and
Conversion), pp. 3277-3282 (2017).
Silica-based Glass
Structures under Extreme Conditions
We are also interested in modeling the
evolution of the internal structures of silica-based
glass/melts under extreme conditions such as under
high-pressure environments. One example of this work is
our collaboration with
Prof. W-Y Ching's group
from UMKC and Prof. Neng Li from State
Key Laboratory of Silicate Materials for Architectures
at Wuhan University in assessing the internal structures
of a pristine silica glass wherein the transition of a
Coordination Number (CN) of 4 to 6 for the SiOx clusters can
also be characterized by a series of changes in the
fundamental properties of the glass with increasing
pressures. More details of the work can be found in
our publication in PCCP.
Neng Li, Ridwan Sakidja, Sitaram Aryal and Wai-Yim Ching,
"Densification of a continuous random network model of amorphous SiO2 glass",
Physical Chemistry Chemical Physics, 16, 1500-1514 (2014)
Silica-based Meso-Porous
Materials
Another important research work in this field is the use of
silica-based amorphous structures to synthesize meso-porous materials
for catalytic applications. We are in close collaboration with
Distinguished Prof. Mayanovic's group at Missouri State and our colleagues at
University of Arkansas, Lehigh University and Cornell University to
assess the stability of the internal structure of these novel materials.
Our
works have been recently published in
MRS Advances and
Microporous and Mesoporous Materials where we investigated the
mechanical and hydrothermal
stability of SBA-15 and
Al-SBA-15 silica-based mesoporous materials under extreme pressures. Here, we closely examined
the mechanical integrity of these materials by means of Molecular Dynamics
(MD) simulations and we compared their modeled structural changes with the results
obtained from the in-situ small angle x-ray
scattering (SAXS) experimental observations.
Evolution of internal cross-sectional structures of
Al-SBA-15 with increasing hydrostatic pressures
Recent publications:
Dayton G. Kizzire, Sonal Dey, Robert A. Mayanovic, Ridwan Sakidja, Kai
Landskron, Manik Mandal, Zhongwu Wang, Mourad Benamara,"Studies
of the Mechanical and Extreme Hydrothermal Properties of Periodic
Mesoporous Silica and Aluminosilica Materials",
Microporous and Mesoporous Materials, Vol. 252, pp. 69–78
(2017).
Dayton G. Kizzire, James Thomas, Sonal Dey, Hayley Osman, Robert A. Mayanovic,
Ridwan Sakidja, Zhongwu Wang, Manik Mandal and Kai Landskron,"Investigations
of the mechanical and hydrothermal stabilities of SBA-15 and Al-SBA-15
mesoporous materials", MRS
Advances, Volume 1, Issue 35 (Materials Design), pp. 2453-2458,
(2016)