Confocal raman microscopy can make a large difference: Resolving and manipulating ferroelectric domains for piezoelectric engineering

Abstract

Ferroelectric materials exhibit spontaneous and stable polarization, which can usually be reoriented by an applied external electric field. The electrically switchable nature of this polarization is at the core of various ferroelectric devices. The following chapter will review the use of Confocal Raman Microscopy (CRM) for the advanced characterization of Lead-free piezoceramics, emphasizing the relationship between structure and piezoelectric properties. In the first part we give a general introduction on the background of the Potassium-Sodium Niobate (KNN) Lead-free piezoceramics for elucidating the phase-structure-performance relationships through a classical approach of Raman spectroscopy. In the second part we reveal the role of the formation of secondary phases in KNN piezoceramics by chemical modifications. This phenomenon is one of the major drawbacks identified in KNN-based systems. In the third part we highlight some practical aspects in the study of ferroelectric domains in KNN-based piezoceramics. Special emphasis is placed on coupling confocal Raman spectroscopy and Atomic Force Microscopy (AFM), demonstrating to being a powerful tool in spatially resolving the structure of ferroelectric domains. Finally, we focus on the light-matter coupling and, consequently, in the relationships between phase boundaries and piezoelectric activity, discuss some existing challenges, suggest possible methods for further improving piezoelectricity, and provide some conclusions.