Tuning the functionalities of a mesocrystal via structural coupling.

Heng-Jui Liu,Jiang-Yu Li,Qing He,Ying-Hao Chu,Chih-Huang Lai,Chien-Te Chen,Hong-Ji Lin,Sheng-Chieh Liao,Yun-Ya Liu,Wen-Feng Hsieh,Ying-Jiun Chen,Chih-Ya Tsai

doi:10.1038/srep12073

Abstract

In the past decades, mesocrystal, a kind of nanocrystals with specific crystallographic orientation, has drawn a lot of attention due to its intriguing functionalities. While the research community keeps searching for new mesocrystal systems, it is equally crucial to develop new approaches to tune the properties of mesocrystals. In this work, a self-organized two-dimensional mesocrystal composed of highly oriented CoFe2O4 (CFO) nano-crystals with assistance of different perovskite matrices is studied as a model system. We have demonstrated that the strain state and corresponding magnetic properties of the CFO mesocrystal can be modulated by changing the surrounding perovskite matrix through their intimate structural coupling. Interestingly, this controllability is more strongly correlated to the competition of bonding strength between the matrices and the CFO mesocrystals rather than the lattice mismatch. When embedded in a matrix with a higher melting point or stiffness, the CFO mesocrystal experiences higher out-of-plane compressive strain and shows a stronger magnetic anisotropy as well as cation site-exchange. Our study suggests a new pathway to tailor the functionalities of mesocrystals.

Highlights

The spontaneously assembled nanopillars possess perfectly ordered crystal-orientation, which can be viewed as a 2-dimenstional (2D) mesocrystal system[6,7,8,9]
Based on the experiences learned from epitaxial systems, we would expect the strain state of the CFO mesocrystal to be strongly correlated to the lattice mismatch with perovskite matrices if they can coherently connect each other
Two white dash lines are marked across these reciprocal space maps (RSMs) at L = 3.000 and L = 2.791, which can be referred to the position of the c-axis lattice of single crystal substrate STO and bulk CFO

Summary

Introduction

The spontaneously assembled nanopillars possess perfectly ordered crystal-orientation, which can be viewed as a 2-dimenstional (2D) mesocrystal system[6,7,8,9]. The matrix materials become very important since they provide additional degrees of freedom to tailor the crystal orientations and physical properties of the mesocrystal, which cannot be observed in those mesocrystals within the organic/polymer matrices. The variation of strain state in the CFO mesocrystal changes its magnetic properties such as a magnetic anisotropy or the origin of magnetic moment in atomic scale. These variations have been discovered to be highly dependent on the bonding strength of the perovskite materials instead of the lattice mismatch between the matrices and the CFO mesocrystal. This study delivers a new concept to design the stress-mediated functionalities of the mesocrystals via the chosen matrix materials

Methods

Results

Conclusion