Metal@SiO₂ Core–Shells with Self-Arrested Migrating Core

Abstract

Developing easy and customizable strategies for the directional structure modulation of multicomponent nanosystems to influence and optimize their properties are a paramount but challenging task in nanoscience. Here, we demonstrate highly controlled eccentric off-center positioning of metal−core in metal@silica core−shells by utilizing an in situ generated biphasic silica-based intraparticle solid− solid interface. In the synthetic strategy, by including Ca 2+ -ions in silica−shell and successive oxidative and reductive annealing at high temperature, a unique hairline−biphasic interface is evolved via the heat-induced concentric radial segregation of calcium silicate phase at the interior and normal silica phase at the exterior of core−shell, which can effectively arrest the outwardly migrating metal−core within rubbery calcium silicate phase, affording various eccentric core−shells, where core-positions are flexibly controlled by the annealing time and amounts of initially added Ca 2+ -ions. In the structure−property correlation study, the strategy allows fine-tuning of dipolar interaction-based blocking temperatures and magnetic anisotropies of different eccentric core−shells as the function of variable off-center distance of magnetic core without changing the overall size of nanoparticles. This work demonstrates the discovery and potential application of biphasic solid−solid media interface in controlling the heat-induced migration of metal nanocrystals and opens the avenues for exploiting the rarely studied high-temperature solid-state nanocrystal conversion chemistry and migratory behavior for directional nanostructure engineering.

Solid-State Reaction Synthesis of Nanoscale Materials: Strategies and Applications

“…). , Apart from the atomic diffusion processes that are common in SSRs, NCs can also migrate while being embedded inside solid-state media, leading to a change in the nature of the interface depending on the surrounding media . Such a migration often inflicts configurational changes in the hybrid structure as a result of changes in the relative positions of different components . Gaining a fundamental understanding of SSRs through a detailed study of the aforementioned diffusion/migration phenomena in different nanoscale systems is highly advantageous to the design and synthesis of new strategies, allowing better structural control and optimization of the properties of functional NMs .…”

Theoretical study of metal/silica interfaces: Ti, Fe, Cr and Ni on β-cristobalite

“…Interaction of metals with oxide and glass substrates has been the subject of studies in the context of various applications, most prominently electronics and catalysis. [1][2][3] More recently, silica/metal interfaces have attracted renewed research attention, focused on novel applications such as strong metal support interaction (SMSI), [4][5][6] metal@SiO 2 core-shell nanoparticles, [7][8][9][10] and techniques for sintering control. 11,12 In addition, metal adhesion to silica and other large gap oxides has emerged as a key challenge for the steel-making industry, as light strengthening elements (Si, Al and Mn) used in modern advanced high strength steels (AHSS) are selectively oxidized during the recrystallization annealing process, with the oxides segregating to the steel surface.…”

Functional Micro/Nanoreactors for Nanospace‐Confined Migrations and Diffusions

“…However, the migration of metal nanocrystals FePd in biphasic matrix CaSiO 3 @SiO 2 is of a little difference. [33] FePd core diffuse outward within the internal CaSiO 3 medium and eventually is Figure 5. (A) Schematic model of the metal clusters diffusion and aggregation in/on the matrix.…”

“…(C) Synthesis of eccentric core‐shells with arrested metal core at the CaSiO 3 −SiO 2 interface. Adapted with permission . Copyright 2019, American Chemical Society.…”

“…With regard to pure phase matrix like silica, metal nanocrystals are inclined to escape to the outermost surface to relieve the high interfacial strain with the unfavorably interacting silica. However, the migration of metal nanocrystals FePd in biphasic matrix CaSiO 3 @SiO 2 is of a little difference . FePd core diffuse outward within the internal CaSiO 3 medium and eventually is arrested at CaSiO 3 −SiO 2 interfacial trap, which avoids the generation of high interfacial energy caused by the relatively unfavorable direct contact of SiO 2 and CaSiO 3 ( Figure C ) .…”