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7. Evaluation of Reverse Monte Carlo Models based on Molecular Dynamics Simulations: A Case Study of Ion Conducting Network Glasses

Author

Mueller, Christian R., Kathriarachchi, Vindu, Schuch, Michael, Maass, Philipp, and Petkov, Valeri

Subjects
Condensed Matter - Materials Science
Abstract

We investigate the quality of structural models generated by the Reverse Monte Carlo (RMC) method in a typical application to amorphous systems. To this end we calculate surrogate diffraction data from a Li2O-SiO2 molecular dynamics (MD) simulation and use the total scattering function, in addition to minimal pair distances and coordination numbers of silicon (oxygen) to oxygen (silicon) ions, as input for the RMC modeling. Then we compare partial radial distribution functions, coordination numbers, bond angles, and ring sizes predicted by the RMC models with those of the MD system. It is found that partial distributions functions and properties on small lengths scales, as distributions of coordination numbers and bond angles, are well reproduced by the RMC modeling. Properties in the medium-range order regime are, however, not well captured, as is demonstrated by comparison of ring size distributions. Due care therefore has to be exercised when extracting structural features from RMC models in this medium-range order regime. In particular we show that the occurrence of such features can be a mere consequence of the chosen starting configuration., Comment: 8 pages, 7 figures

Published
2009

16. Simple Synthesis of Monodisperse Ultrasmall Au Icosahedral Nanoparticles

Author

Yildirim, Ezgi, primary, Ramamoorthy, Raj Kumar, additional, Parmar, Rohan, additional, Roblin, Pierre, additional, Vargas, Jorge A., additional, Petkov, Valeri, additional, Diaz, Ana, additional, Checchia, Stefano, additional, Ruiz, Isaac Rodriguez, additional, Teychené, Sébastien, additional, Lacroix, Lise-Marie, additional, and Viau, Guillaume, additional

Published
2023
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19. Investigating the Role of Vacancies on the Thermoelectric Properties of EuCuSb‐Eu2ZnSb2 Alloys.

Author

Chanakian, Sevan, Peng, Wanyue, Meschke, Vanessa, Ashiquzzaman Shawon, A. K. M., Adamczyk, Jesse, Petkov, Valeri, Toberer, Eric, and Zevalkink, Alexandra

Subjects
THERMOELECTRIC materials, CARRIER density, ATOMIC displacements, BAND gaps, POINT defects
Abstract

AMX compounds with the ZrBeSi structure tolerate a vacancy concentration of up to 50 % on the M‐site in the planar MX‐layers. Here, we investigate the impact of vacancies on the thermal and electronic properties across the full EuCu1−xZn0.5xSb solid solution. The transition from a fully‐occupied honeycomb layer (EuCuSb) to one with a quarter of the atoms missing (EuZn0.5Sb) leads to non‐linear bond expansion in the honeycomb layer, increasing atomic displacement parameters on the M and Sb‐sites, and significant lattice softening. This, combined with a rapid increase in point defect scattering, causes the lattice thermal conductivity to decrease from 3 to 0.5 W mK−1 at 300 K. The effect of vacancies on the electronic properties is more nuanced; we see a small increase in effective mass, large increase in band gap, and decrease in carrier concentration. Ultimately, the maximum zT increases from 0.09 to 0.7 as we go from EuCuSb to EuZn0.5Sb. [ABSTRACT FROM AUTHOR]

Published
2023
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25. Lattice Strain and Surface Activity of Ternary Nanoalloys under the Propane Oxidation Condition

Author

Kareem, Haval, primary, Maswadeh, Yazan, additional, Wu, Zhi-Peng, additional, Leff, Asher C., additional, Cheng, Han-Wen, additional, Shan, Shiyao, additional, Wang, Shan, additional, Robinson, Richard, additional, Caracciolo, Dominic, additional, Langrock, Alex, additional, Mackie, David M., additional, Tran, Dat T., additional, Petkov, Valeri, additional, and Zhong, Chuan-Jian, additional

Published
2022
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28. Studier av termisk degradering i härdplastpolyimider och dess kompositer

Author

Petkov, Valeri

Subjects
Polymer composites, Textil-, gummi- och polymermaterial, Thermal oxidative degradation, Textile, Rubber and Polymeric Materials, Kompositmaterial och -teknik, Composite Science and Engineering, Polyimide
Abstract

The thesis contains a background and reflections section, an introduction, and three appended articles. The first section is reserved for some of the background and basics on polymers and polymer composites and a discussion on their effect on our everyday lives. The introduction gives a brief recap of the project. The articles contain the research that was performed on the thermal oxidation of thermosetting polyimides and their composites during the project. The first article covered the thermal oxidative degradation of satin weave and thin-ply composites made by resin transfer molding with carbon fibers and thermosetting polyimide. The degradation was studied by weight loss measurements and X-ray computed microtomography. The weight loss measurements showed that the initial desorption stage during ageing followed Fickian behavior and the proposed model. It was also observed that the satin weave composites formed crack clusters that grew into a network of cracks, voids and delaminations throughout the specimens as the ageing time progressed, while the thin-ply composites only formed delaminations at the free edges. The second manuscript studied the behavior of the neat polyimide resin when aged for up to 1500 hours in ambient air, and compared it with a newly developed polyimide formulation, with slightly altered chemical composition. The reduced amount of internal crosslinkers in the newer formulation was expected to enhance the fracture toughness of the material. Three-point bending, differential scanning calorimetry, dilatometry, weight loss, light optical microscopy and nanoindentation experiments were performed and highlighted the differences in the thermal and mechanical properties of the two formulations. A slight increase in the fracture toughness was observed, while the glass transition of the new formulation had decreased. The third manuscript was aimed at continuing the discussion from the second article on the differences between the two thermosetting polyimides. Thermogravimetric scans showed that the polyimide formulations behaved very similarly under thermal oxidative tests. The initial analysis gave indications that the model could capture well the degradation at high temperatures, but is not adequate in predicting long-term degradation at temperatures around 288–400 °C.

Published
2022

30. The Influence of Ethynyl In-Chain Crosslinkers on the Properties of 6FDA-Based Polyimides.

Author

Petkov, Valeri Ivanov, Pelcastre, Leonardo, Solano, Carlos, and Fernberg, Patrik

Subjects
*MECHANICAL behavior of materials, *POLYIMIDES, *FRACTURE toughness, *POLYMER liquid crystals, *DIFFERENTIAL scanning calorimetry, *THERMAL properties, *GLASS transition temperature
Abstract

Two 4,4′-(hexafluoroisopropylidene)diphthalic anhydride-based thermosetting polyimide formulations with varied amounts of crosslinking sites were compared to understand the influence of crosslinking density on fracture toughness, glass transition temperature and thermal oxidative stability. The thermal and mechanical properties of both materials were investigated through a series of single-edge notched beams, differential scanning calorimetry, dilatometry, weight loss, light optical microscopy and nanoindentation experiments. It was found out that the reduced crosslinking resulted in slightly increased fracture toughness but decreased the Tg of the material. No significant difference could be observed in the thermal oxidative stability with the experimental techniques considered. [ABSTRACT FROM AUTHOR]

Published
2023
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34. Highly reversible Zn metal anode enabled by sustainable hydroxyl chemistry.

Author

Lin Ma, Vatamanu, Jenel, Hahn, Nathan T., Pollard, Travis P., Borodin, Oleg, Petkov, Valeri, Schroeder, Marshall A., Yang Ren, Ding, Michael S., Chao Luo, Allen, Jan L., Chunsheng Wang, and Kang Xu

Subjects
SUSTAINABLE chemistry, NONAQUEOUS solvents, HYDROGEN evolution reactions, ENERGY storage, ORGANIC products, ANODES
Abstract

Rechargeable Zn metal batteries (RZMBs) may provide a more sustainable and lower-cost alternative to established battery technologies in meeting energy storage applications of the future. However, the most promising electrolytes for RZMBs are generally aqueous and require high concentrations of salt(s) to bring efficiencies toward commercially viable levels and mitigate water-originated parasitic reactions including hydrogen evolution and corrosion. Electrolytes based on nonaqueous solvents are promising for avoiding these issues, but full cell performance demonstrations with solvents other than water have been very limited. To address these challenges, we investigated MeOH as an alternative electrolyte solvent. These MeOH-based electrolytes exhibited exceptional Zn reversibility over a wide temperature range, with a Coulombic efficiency > 99.5% at 50% Zn utilization without cell short-circuit behavior for > 1,800 h. More important, this remarkable performance translates well to Zn ∥ metal-free organic cathode full cells, supporting < 6% capacity decay after > 800 cycles at -40 °C. [ABSTRACT FROM AUTHOR]

Published
2022
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37. High Pressure Nitrogen-Infused Ultrastable Fuel Cell Catalyst for Oxygen Reduction Reaction

Author

Lee, Eunjik, primary, Kuttiyiel, Kurian A., additional, Kim, Kyoung-Hee, additional, Jang, Jeongyun, additional, Lee, Hyo J., additional, Lee, Jong M., additional, Seo, Min H., additional, Yang, Tae-Hyun, additional, Yim, Sung-Dae, additional, Vargas, Jorge A., additional, Petkov, Valeri, additional, Sasaki, Kotaro, additional, Adzic, Radoslav R., additional, and Park, Gu-Gon, additional

Published
2021
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42. Alloying–Realloying Enabled High Durability for Pt–Pd–3d-Transition Metal Nanoparticle Fuel Cell Catalysts

Author

Wu, Zhipeng, primary, Maswadeh, Yazan, additional, Wen, Jianguo, additional, Kong, Zhijie, additional, Shan, Shiyao, additional, Vargas, Jorge, additional, Yan, Shan, additional, Hopkins, Emma, additional, Park, Keonwoo, additional, Sharma, Anju, additional, Ren, Yang, additional, Petkov, Valeri, additional, Wang, Lichang, additional, and Zhong, Chuan-Jian, additional

Published
2020
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43. Structure of nanocrystalline alkali metal manganese oxides by the atomic pair distribution function technique

Author

Gateshki, Milen, Seong-ju Hwang, Park, Dae Hoon, Yang Ren, and Petkov, Valeri

Subjects
Alkali metals -- Atomic properties, X-rays -- Diffraction, X-rays -- Usage, Chemicals, plastics and rubber industries
Abstract

The atomic scale structure of two nanocrystalline K-Li-Mn-O-I materials obtained through Chimie Douce route in aqueous and acetone solutions are determined by using X-ray diffraction and atomic Pair Distribution Function technique. Some methodological aspects of the atomic pair distribution function technique and its applicability to study the structure of crystalline and nanocrystallinematerilas are described.

Published
2004

45. Structure of V2O5.nH2O xerogel solved by the atomic pair distribution function technique

Author

Petkov, Valeri; Kanatzidis, Mercouri G., Trikalitis, Pantelis N., Bozin, Emil S., Billinge, Simon J.L., and Vogt, Thomas

Subjects
Molecular structure -- Research, Molecules -- Research, Chemistry
Abstract

The full three-dimensional structure of the lamellar turbostratic V2O5.nH2O xerogel was determined by the atomic pair distribution. It is shown that on the atomic scale the slabs of the xerogel can be described well as almost perfect pairs (that is bilayers) of single V2O5 layers made of square pyramidal VO5 units.

Published
2002

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