Surface hydration-mediated conduction of NiO nanocrystals

In this work, we initiated an investigation on the conduction behavior of NiO nanocrystals. All as-prepared NiO nanocrystals were terminated with hydration layers at ambient conditions. With increasing the temperature up to 393 K, the hydration layers of NiO nanocrystals decreased. Alternative current and direct current conductivity measurements coupled with thermogravimetric analysis confirmed that there exists proton conduction in the surface hydration layers and hole conduction in the bulk for small particle sizes of NiO nanocrystals. The removal of hydration layers from the NiO surfaces gave rise to a reduction in the bulk and grain boundary conductivities. With increasing the particle size, the bulk conduction showed an activation energy minimum, which was interpreted in terms of variations of charge carrier concentration and the hopping distance between the charge carriers.