Photostrictive/Piezomagnetic Core–Shell Particles Based on Prussian Blue Analogues: Evidence for Confinement Effects?

Abstract

High-quality core–shell particles, which associate a photostrictive core (Rb0.5Co­[Fe­(CN)6]0.8·zH2O, RbCoFe) and a ferromagnetic shell (Rb0.2Ni­[Cr­(CN)6]0.7·z′H2O, RbNiCr), were successfully grown by a multistep protocol based on coprecipitation in water. High-resolution transmission electron microscopy shows that well-defined heterostructures are formed and that the core–shell interface is abrupt with the epitaxial relationship [001](001)RbCoFe//[001]­(001)RbNiCr, confirmed by simulations of the X-ray diffraction line widths. The core particles are monocrystalline, with 50 nm sides, and the shell consists of large platelet-like crystallites, with a height that corresponds to the shell thickness and lateral dimensions comparable to the size of the core particles. Analysis of the diffracted intensities as a function of shell thickness (9–26 nm) shows that the epitaxial shell growth does not lead to a thick pseudomorphic layer at the interface. In contrast, Williamson–Hall plots suggest that a structural relaxation takes place to adapt the mismatched lattices, with the formation of misfit dislocations distributed over the entire shell thickness. This later finding is indicative of an effective mechanical coupling within the heterostructures. However, a magnetization increase by only a few percent was observed under light irradiation for these RbCoFe@RbNiCr particles. We showed from in situ synchrotron X-ray diffraction measurements that these small changes most likely reflect confinement effects as photoswitching of the core phase is partly or completely blocked depending on the shell thickness.

Elasticity of Prussian‐Blue‐Analogue Nanoparticles

“…Access to the elastic moduli of PBA nanoparticles, which are largely unknown in molecule-based materials (bulk and nano-object), is of paramount importance for developing applications based on the mechanical properties of molecular materials, such as microelectromechanical systems (MEMS) [36,37] or mechanically coupled nano-heterostructures. [22,24,38] It is important to stress also that in this work, we provide an accurate value of Poisson's ratio. The mechanical characterization of coordination networks is challenging, especially at the nanoscale, but it is necessary for the development of new applications and for understanding phase-change phenomena governed by electron-lattice coupling.…”

“…When one of the components undergoes an electronic phase transition, this coupling can even allow the switching of the properties of the second component. [22,24] Theoretical analysis has highlighted that the pressure the core (shell) can apply to the shell (core) upon the phase transition can be estimated if Young's moduli and Poisson's ratios of both components are known. [25] Then, combining the theoretical prediction with synthetic control of the core and shell thicknesses, the applied pressure on the core and the shell can be controlled, opening the way to monitoring the synergy between magnetism, optical, and electronic phenomena in PBA heterostructures.…”

Spin Crossover Nanomaterials: From Fundamental Concepts to Devices

“…This latter is related in most cases to a charge transfer between the cyanide‐bridged metallic centers, denoted charge transfer induced spin transition (CTIST), which can occur due to thermal, pressure, or light stimuli . Recently, the groups of Mallah, Talham, and Maurin succeeded in synthesizing fairly monodisperse core–shell PBA@PBA nanoparticles with a CoFe core exhibiting CTIST and an epitaxial ferromagnetic shell consisting of either NiCr or CoCr analogs. Their experiments revealed in each case remarkable couplings between the properties of the constituents.…”

New faces of porous Prussian blue: interfacial assembly of integrated hetero-structures for sensing applications

“…36 For the pulse reverse deposition strategy, PB heterointerfaces were obtained by stepping the electrode potential between two different potentials with a periodic pulse frequency. 12,[99][100][101] In recent years, the universality of classical crystallization has been questioned upon investigations of crystal growth processes for assembly of Prussian blue, and few examples have shown that crystal growth may not follow such a classical crystallization process. Interfacial assembly by seed mediated growth A classical crystallization process starts from stable nuclei followed by a simple enlargement of the nuclei by unit-cell replication.…”