Raman shift, Néel temperature, and optical band gap of NiO nanoparticles

With structural miniaturization down to the nanoscale, the detectable parameters of materials no longer remain constant but become tunable. For NiO nanoparticles example, Raman shift and Neel temperature increase while optical band gap decreases with increasing the nanoparticle size. Herein, we developed the models to describe the size dependence of these seemingly uncorrelated parameters for NiO nanoparticles, based on the average coordination number-dependent cohesive energy model. Consistency between our theoretical predictions and the corresponding experimental results not only verified the accuracy of our developed models but also provided insight into the essentiality of cohesive energy in describing the effect of size on the materials properties of NiO nanoparticles.