Strategy to control magnetic coercivity by elucidating crystallization pathway-dependent microstructural evolution of magnetite mesocrystals

Abstract

Mesocrystals are assemblies of smaller crystallites and have attracted attention because of their nonclassical crystallization pathway and emerging collective functionalities. Understanding the mesocrystal crystallization mechanism in chemical routes is essential for precise control of size and microstructure, which influence the function of mesocrystals. However, microstructure evolution from the nucleus stage through various crystallization pathways remains unclear. We propose a unified model on the basis of the observation of two crystallization pathways, with different ferric (oxyhydr)oxide polymorphs appearing as intermediates, producing microstructures of magnetite mesocrystal via different mechanisms. An understanding of the crystallization mechanism enables independent chemical control of the mesocrystal diameter and crystallite size, as manifested by a series of magnetic coercivity measurements. We successfully implement an experimental model system that exhibits a universal crystallite size effect on the magnetic coercivity of mesocrystals. These findings provide a general approach to controlling the microstructure through crystallization pathway selection, thus providing a strategy for controlling magnetic coercivity in magnetite systems.

Surface-ligand-induced crystallographic disorder–order transition in oriented attachment for the tuneable assembly of mesocrystals

“…The polymorphism of ferric oxyhydroxide as an intermediate significantly affects the crystallisation mechanism of Fe 3 O 4 mesocrystals 17 , 18 , 23 – 25 . We recently identified two Fe 3 O 4 crystallisation pathways starting from either lepidocrocite or goethite and revealed that Fe 3 O 4 mesocrystals grew via OA only in the former case 23 . These pathways are competitively responsible for Fe 3 O 4 growth and can be selectively regulated according to the initial [OH – ]/[Fe 3+ ] ratio.…”

Boosting the Catalytic Performance of CeO2 in Toluene Combustion via the Ce–Ce Homogeneous Interface

“…Surface oxygen vacancies can serve as the activation sites of O 2 molecules, probably reducing the energy barrier of oxygen species regeneration. Meanwhile, the Ce–Ce homogeneous interface and bulk oxygen vacancies reduce the activation and migration barriers of reactive oxygen species . Therefore, CeO 2 –MC tends to exhibit much better catalytic performance.…”

“…Meanwhile, the Ce−Ce homogeneous interface and bulk oxygen vacancies reduce the activation and migration barriers of reactive oxygen species. 53 Therefore, CeO 2 −MC tends to exhibit much better catalytic performance.…”

Direct and Indirect Nucleation of Magnetite Nanoparticles from Solution Revealed by Time-Resolved Raman Spectroscopy

“…The oxolation process is the formation of oxo bridges (−Fe–O–Fe−) accompanied by expelling of molecular water . The primary colloidal particles then aggregate, which allows the heterogeneous nucleation of anhydrous iron oxides, including MNPs. ,,,,− This advanced model for magnetite nucleation has been proposed based on data acquired from time-resolved and/or conventional measurements using sophisticated analytical/reactor tools such as liquid-cell transmission electron microscopy (TEM), cryo-TEM, microfluidic reactors, titration reactors, dynamic light scattering, analytical ultracentrifugation, synchrotron-based X-ray diffraction (XRD), small- and wide-angle X-ray scattering (SAXS/WAXS), atomic force microcopy, and field-emission scanning electron microscopy (FESEM). In these experimental studies, direct nucleation of MNPs from ionic solutions has been rarely invoked and measured. , Two main approaches have been proposed to explain the formation of magnetite.…”