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

With structural miniaturization down to the nanoscale, some detectable parameters of materials no longer remain constant. For NiO nanoparticles example, Raman shift and Néel temperature increase while optical band gap decreases with increasing the nanoparticle size. Herein, we developed the analytic models to describe the size dependence of these above-mentioned 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.