3. Nanostructured Materials

As discussed in the previous chapter, the study of piezoelectric materials dates back over a century, and a huge number of different materials displaying piezoelectric behaviour have been demonstrated. However, to date there has been relatively limited use of nanostructured piezoelectric materials in functioning devices. This is partly because understanding of the nanoscale size effects on ferro- and piezoelectricity is still being developed, as discussed in Sect. 2.3.4. It is also because production of nano-sized structures of piezoelectric materials often involves complex processing either due to the ternary, quaternary or higher number of elements combined in specific quantities, or the ceramic nature of a number of piezoelectric materials, requiring high processing temperatures. However, there are some exceptions to this, the most well known being zinc oxide (ZnO). As discussed below, a number of simple methods have been extensively studied for the production of nanoscale ZnO, and as such it is the most widely used material in piezoelectric nanogenerators. However, other well-known materials have also been investigated including lead zirconate titanate (PZT) and barium titanate. In this chapter the synthesis methods used to produce these materials are summarised, and details of the development and specific examples of piezoelectric nanogenerators are described.