Generating MnO2 Nanoparticles Using Simulated Amorphization and Recrystallization

• Published in: Journal of the American Chemical Society Vol. 127; no. 37; pp. 12828 - 12837
• Main Authors: Sayle, Thi X. T, Catlow, C. Richard A, Maphanga, R. Regina, Ngoepe, Phuti E, Sayle, Dean C
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 21.09.2005
• Subjects: Cross-disciplinary physics: materials science; rheology; Crystallization; Crystallography, X-Ray; Exact sciences and technology; Manganese Compounds - chemistry; Materials science; Methods of crystal growth; physics of crystal growth; Models, Molecular; Nanostructures - chemistry; Oxides - chemistry; Physics; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation; Time Factors; Amorphization crystallization; Manganese oxides; Radial distribution function; Molecular dynamics method; Theoretical study; Transition elements Compounds; Crystal nucleation; Dynamical recrystallization; Crystal morphology; Submicron particle
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0434073

Models of MnO2 nanoparticles, with full atomistic detail, have been generated using a simulated amorphization and recrystallization strategy. In particular, a 25,000-atom “cube” of MnO2 was amorphized (tension-induced) under molecular dynamics (MD). Long-duration MD, applied to this system, results in the sudden evolution of a small crystalline region of pyrolusite-structured MnO2, which acts as a nucleating “seed” and facilitates the recrystallization of all the surrounding (amorphous) MnO2. The resulting MnO2 nanoparticle is about 8 nm in diameter, conforms to the pyrolusite structure (isostructural with rutile TiO2, comprising 1 × 1 octahedra) is heavily twinned and comprises a wealth of isolated and clustered point defects such as cation vacancies. In addition, we suggest the presence of ramsdellite (2 × 1 octahedra) intergrowths. Molecular graphical snapshots of the crystallization process are presented.