Chen Xiaodan, van Gog Heleen, van Huis Marijn A
Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University Princetonplein 5 3584 CC Utrecht The Netherlands
Engineering Thermodynamics, Process & Energy Department, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology Leeghwaterstraat 39 2628 CB Delft The Netherlands
J Mater Chem C Mater. 2021 Mar 27;9(17):5662-5675. doi: 10.1039/d0tc05727d.
Nanoparticles of CoO and CoO are of paramount importance because of their chemical properties propelling their applications in catalysis and battery materials, and because of their intriguing magnetic properties. Here we elucidate the transformation of CoO nanoparticles to CoO into nanoscale detail by heating in the transmission electron microscope (TEM), and we decipher the energetics and magnetic properties of the CoO/CoO interface from first principles calculations. The transformation was found to start at a temperature of 350 °C, and full conversion of all particles was achieved after heating to 400 °C for 10 minutes. The transformation progressed from the surface to the center of the nanoparticles under the formation of dislocations, while the two phases maintained a cube-on-cube orientation relationship. Various possibilities for magnetic ordering were considered in the density functional theory (DFT) calculations and a favorable CoO/CoO {100}/{100} interface energy of 0.38 J m is predicted for the lowest-energy ordering. Remarkably, the DFT calculations revealed a substantial net ferromagnetic moment originating from the interface between the two antiferromagnetic compounds, amounting to approximately 13.9 nm. The transformation was reproduced when heating at a temperature of 400 °C in a high vacuum chamber.
由于其化学性质推动了它们在催化和电池材料中的应用，以及其引人入胜的磁性，氧化钴（CoO）纳米颗粒至关重要。在此，我们通过在透射电子显微镜（TEM）中加热，详细阐释了CoO纳米颗粒向CoO的转变过程，并从第一性原理计算中解读了CoO/CoO界面的能量学和磁性。发现转变始于350°C的温度，在加热至400°C持续10分钟后，所有颗粒实现了完全转化。转变从纳米颗粒的表面向中心进行，同时形成位错，而两相保持立方对立方的取向关系。在密度泛函理论（DFT）计算中考虑了各种磁有序的可能性，预测对于最低能量有序状态，有利的CoO/CoO {100}/{100}界面能为0.38 J/m²。值得注意的是，DFT计算揭示了源自两种反铁磁化合物界面的显著净铁磁矩，约为13.9 μB。在高真空室中于400°C加热时，该转变得以重现。
