Theoretical study of the structural and energetic properties of Ce_1-xZr_xO₂ nanoparticles via molecular dynamics simulations

Author(s)

Santos, Mylena N. ; Lourenco, Tuanan C. ; Mocelim, Mauricio ; Da Silva, Juarez L. F.

• Document type: Journal article
• Source: Physical Chemistry Chemical Physics; v. 26, n. 25, p. 16-pg., 2024-05-20.

Abstract

The combination of ceria (CeO2) with different metal oxides (MO2), e.g. Ce1-xMxO2, has been strategically used to enhance its intrinsic properties. Moreover, the controlled synthesis of mixed oxide nanoparticles (NPs) opens the opportunity to explore the size dependence and chemical composition of the physical-chemical properties. However, our atomic-level understanding of how the physical-chemical and thermodynamic characteristics change with particle size and composition remains far from satisfactory. Here, we used force-field molecular dynamics simulations to investigate the effects of composition (x) and size on the physical-chemical properties of Ce1-xZrxO2 NPs with diameter from 1 (32 cations) up to 3 nm (256 cations), where x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0. We found abrupt changes in potential energy versus temperature for NPs with more than 108 cations, indicating a structural phase transition from disordered to ordered structures, which was confirmed by the radial distribution function. We found a linear relationship between the phase transition temperature (T-pt) and the size and composition of the NPs: the increase in the molar fraction of Zr4+ and the reduction in particle size are related to lower T-pt temperature and less defined decays of potential energy versus temperature. NPs larger than 56 cations show a radial distribution function with several peaks, which is related to the order of cations and anions in these structures. These peaks gradually disappear as the size decreases and the fraction of Zr4+ increases. Similar trends were observed with X-ray diffraction analysis; for example, fluorite-like motifs occur even with 56 cations in the case of ceria, but only for NPs with 108 cations for zirconia. Common neighbor analysis confirmed that NPs with well-defined values of the temperature T-pt have face-centered cubic (fcc)-like domains in the core region. The number of ordered fcc cations increases with increasing NP size and decreasing Zr4+ concentration. Finally, we observed that ceria nucleate first during simulated annealing and occupy highly coordinated sites within the core, while Zr4+ prefers the lowest coordinated sites on the surface. (AU)

• FAPESP's process: 19/23681-0 - From ab initio to continuum methods to the screening of sodium-ion battery materials
• Grantee: Tuanan da Costa Lourenço
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 18/21401-7 - Multi-User Equipment approved in grant 2017/11631-2: cluster computational de alto desempenho - ENIAC
• Grantee: Juarez Lopes Ferreira da Silva
• Support Opportunities: Multi-user Equipment Program
• FAPESP's process: 22/05652-5 - Polarizable force fields for the Investigation of sodium-ion battery materials
• Grantee: Tuanan da Costa Lourenço
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• FAPESP's process: 20/10532-3 - Study of the structural and energetic properties of nanoligas formed by CeO2-ZrO2 via molecular dynamics calculations
• Grantee: Mylena Novaes Santos
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• FAPESP's process: 17/11631-2 - CINE: computational materials design based on atomistic simulations, meso-scale, multi-physics, and artificial intelligence for energy applications
• Grantee: Juarez Lopes Ferreira da Silva
• Support Opportunities: Research Grants - Research Centers in Engineering Program