On the prediction of external shape of ZnO nanocrystals

From ancient times, minerals have been recognized by their distinct external shapes. Very recently, there is a growing interest towards shape control of nanocrystals and microcrystals as various properties like optical, electrical and magnetic are greatly influenced by their external shape. ZnO nanocrystals find various applications in physics, optics, medicine, and electronics. Predicting equilibrium shape of ZnO nanocrystals is an important step to judge their capability in different uses for instance in drug delivery or energy storage. However, predicting morphology for ZnO nanocrystals is tedious, because ZnO crystalline material grows with a diverse range of external shapes. In present report, external morphology of ZnO crystal is deduced from its internal crystal structure by considering the propagation vector of center of mass of the molecular basis (namely HNB vector; Harsh - Nidhi - Binay) in the ZnO lattice. Also, two of the well established models namely Bravais - Friedel - Donnay - Harker model (BFDH), and Hartman - Perdok (HP) periodic-bound chain (PBC) vectors model were used to predict morphology of ZnO crystal. The results of all the three models are compared against the experimentally observed morphologies of ZnO nanoparticles by various research groups. Results suggest that the morphology predicted by BFDH law, HP theory and HNB theory completely agrees with the actual grown ZnO crystal shape by different research groups as well as proves the diversity in the external shape of ZnO nanocrystals.