Structural Core-Shell beyond Chemical Homogeneity in Non-Stoichiometric Cu5FeS4 Nano-Icosahedrons: An in Situ Heating TEM Study.

Bin Zhang,Xiao Zhang,Xiaowei Zhao,Tianrui Dong,Xiaoyuan Zhou,Aijuan Zhang,Guang Han

doi:10.3390/nano10010004

Abstract

Thermal stability of core-shell structured nanoparticles is of vital importance to their practical applications at elevated temperature. Understanding the evolution of chemical distribution and the crystal structure of core-shell nanostructures with temperature variation at the nanoscale will open the route for practical applications and property enhancement of nanoparticles through proper design of new nanomaterials. In this study, core-shell non-stoichiometric Cu5FeS4 icosahedral nanoparticles were investigated by in situ heating transmission electron microscopy. Compared to the high structural and compositional stability at room temperature, the interdiffusion of Cu and Fe atoms became significant, ending up with disappearance of chemical difference in the core and shell over 300 °C. In contrast, different crystal structures of the core and shell were preserved even after heating at 350 °C, indicating the high structural stability. The inconsistency between chemical composition and crystal structure should be ascribed to the interaction between the intrinsic strain existing in the icosahedrons and various structures of this material system. In other words, the geometrically intrinsic strain of the nano-icosahedrons is helpful to modulate/maintain the core-shell structure. These findings open new opportunities for revealing the thermal stability of core-shell nanostructures for various applications and are helpful for the controllable design of new core-shell nanostructures.

Highlights

In recent years, core-shell nanostructures have attracted extensive attention for catalysis [1], energy conversion/storage [2,3], sensors [4], structure/property modifications [5], and so on because of their outstanding optical and electrical properties
The procedures for synthesis of Cu5 FeS4 core-shell icosahedral nanoparticles were described in detail in our previous work [27]
Ultramicrotomy was applied to section nanoparticles into thin slices for high-resolution TEM (HRTEM) observation and composition determination for cores and shells, since the nanoparticles with a size of 100–200 nm were too large/thick for these studies

Summary

Introduction

Core-shell nanostructures have attracted extensive attention for catalysis [1], energy conversion/storage [2,3], sensors [4], structure/property modifications [5], and so on because of their outstanding optical and electrical properties. Practical applications is stability, especially under high-temperature conditions. With typical sizes down to nanometer scale, the proportion of surface atoms is significantly increased; nanomaterials often reveal tremendous surface effects but reduced stability compared with bulk materials. More occur at elevated temperatures for nanomaterials. High temperature and related treatment often disturbs/changes the core-shell structures that will, in turn, affect the performance and applications of core-shell nanostructures. Structural, and compositional evolution of nanomaterials (e.g., core-shell nanostructures) during the thermal process is of vital

Methods

Results

Conclusion