Ferroelectric and piezoelectric oxide nanostructured films for energy harvesting applications

Perovskite oxide materials have been widely investigated due to properties related to their spontaneous polarization such as ferroelectricity, piezoelectricity, and pyroelectricity. Often due to high chemical stability, and mechanical robustness with large dielectric constants, ferroelectric and piezoelectric perovskite oxides have become essential components in a wide spectrum of applications such as nonvolatile random access memory, microelectromechanical devices, sensors, actuators, high-frequency electrical components, tunable microwave circuits, nanogenerators for energy harvesting, and as potential solar-cell absorbers. The realization of miniaturized devices has required these materials to be investigated in thin-film forms. However, research in ferroelectric and piezoelectric thin films is limited due to the intrinsic difficulties of structural engineering at the nanoscale. To this end, nanostructured films exhibit uniquely different properties from nontextured homogenous thin films due to the deliberate engineering of nanoscale features into the structure. Moreover, nanostructuring provides new insights into the size, shape, and surface effects on the charge-ordering in ferroelectric and piezoelectric perovskite oxide materials. The down-scaling effect results in an enhancement of the surface area of materials where surface charges play a dominant role in determining the magnitude and direction of polarization. As polarization properties are the cumulative phenomenon of crystal dimensions, orientation, and ordering, synthesis methodologies that can lead to the manipulation of size and dimensions of ferro- and piezoelectric nanostructures can offer great advantages. However, the large-scale synthesis and integration of ordered functional nanowires is a challenge, due to their complicated fabrication methodologies, high cost, and difficulties with phase stability in many metastable perovskite compounds. In this chapter we will review how facile solution-based synthesis processes can be utilized for fabricating state-of-the art and novel perovskite nanostructured films where tuning crystallinity and strain engineering due to interfacial effects, dimensional confinement, and domain wall interaction resulting from grain boundaries in nanostructures may enhance the Curie temperature, permittivity, or polarizability, and induce “self-poling” effects, eventually enhancing the overall performance of the devices. We will also consider the potential of some of the new ferroelectric nanostructures for photovoltaic applications, proposing pathways for coherent design of next-generation sustainable energy devices.