Aluminum hydrate dehydration interfaces were studied using a van der Waals density functional. The interface configurations investigated here as a first exploration of possible interface geometries, were all found to have a reasonable probability of occurring. From gibbsite/boehmite and boehmite/γ-Al2O3 interface simulation cells, the formation of dehydration-related defects during relaxation was observed. H transfer between hydroxyl groups, and separation of hydroxyl groups and H atoms from the lattice, resulted in the formation of chemisorbed H2O and OH2 groups in gibbsite; in boehmite, the formation of OH2 groups and interstitial H was observed. All interfaces show a transfer of small amounts of charge across the interface. Accumulation of charge in spaces interstitial to the lattice was found to play a role in the dehydration process as well. The present study shows the potential of interface studies for elucidating dehydration pathways at the atomic scale, and offers various starting-points for follow-up studies.@en

Nanoparticles of Co3O4 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 Co3O4 nanoparticles to CoO into nanoscale detail by in situ heating in the transmission electron microscope (TEM), and we decipher the energetics and magnetic properties of the Co3O4/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 Co3O4/CoO {100}/{100} interface energy of 0.38 J m-2 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 μB nm-2. The transformation was reproduced ex situ when heating at a temperature of 400 °C in a high vacuum chamber. This journal is @en

Thermally induced structural transformation of 2D materials opens unique avenues for generating other 2D materials by physical methods. Imaging these transitions in real time provides insight into synthesis routes and property tuning. We have used in situ transmission electron microscopy (TEM) to follow thermally induced structural transformations in layered CoSe2. Three transformation processes are observed: orthorhombic to cubic-CoSe2, cubic-CoSe2 to hexagonal-CoSe, and hexagonal to tetragonal-CoSe. In particular, the unit-cell-thick orthorhombic structure of CoSe2 transforms into cubic-CoSe2 via rearrangement of lattice atoms. Cubic-CoSe2 transforms to hexagonal-CoSe at elevated temperatures through the removal of chalcogen atoms. All nanosheets transform to basal-plane-oriented hexagonal 2D CoSe. Finally, the hexagonal to tetragonal transformation in CoSe is a rapid process wherein the layered morphology of hexagonal-CoSe is broken and islands of tetragonal-CoSe are formed. Our results provide nanoscopic insights into the transformation processes of 2D CoSe2 which can be used to generate these intriguing 2D materials and to tune their properties by modifying their structures for electro-catalytic and electronic applications.@en