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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:

Boron Carbide

 

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.

Figure 1 

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)