A review on piezo-/ferro-electric properties of morphologically diverse ZnO nanostructures

The observation of feeble ferroelectricity and giant piezoelectricity in doped II–VI ZnO binary semiconductor has inspired a great deal of research interest, which could pave the way to reduce the toxic effects on the environment, and to develop small molecule ferroelectrics and flexible piezoelectric nanogenerator. The main challenge for practical application of the ZnO is the attainment of a high Curie temperature to be compatible with junction temperatures. This review focuses primarily on the piezoelectric and ferroelectric properties of zinc oxide (ZnO) nanostructures. One of the desirable outcomes is to provide a useful insight into various processes which may induce ferroelectricity and enhance piezoelectricity in non-ferroelectric and weak piezoelectric ZnO. Taking into consideration the recent progress in this area, topics such as local switchable polarization, effects of defects, ionic charge of the dopant and ionic size of the dopant, and their contributions to piezoelectric and ferroelectric properties of ZnO are discussed. A critical review of the question dealing with the origin of ferroelectricity in ZnO is given. In a similar vein, methods for enhancing piezoelectric coefficient of ZnO are briefly discussed, followed by their applications in potential devices. From this review, it can be concluded that ZnO (a lead-free and biocompatible material) on being doped with suitable dopants show king-sized piezoelectric response and feeble ferroelectric response, which possibly make ZnO an attractive alternative to lead based perovskites for specific applications. This subject is of current interest to various scientists worldwide and hence, motivated us to write a review article with an aim that it would give further momentum to the scientists already working in this field.