High spatial resolution structure of (K,Na)NbO3 lead-free ferroelectric domains

In this paper, we highlight some practical aspects in the study of ferroelectric domains in lead-free (K,Na)NbO3 piezoceramics. This work presents and discusses the spatial resolved structure of the ferroelectric domain existing in (K,Na)NbO3 based ceramics studied by confocal Raman microscopy (CRM) coupled with atomic force microscopy. In addition to the domain identification, CRM allows a determination of the nature of domain walls and correlation between the structure and piezoelectric properties. The tetragonal constraint for orthorhombic domain formations is demonstrated by this technique. Alternating polarization differences in 180 degrees domain templates are resolved by 60 degrees and 120 degrees domains. The internal stress results in the appearance of an unusual polarization relaxation at the 90 degrees domain wall in (K,Na)NbO3 ceramics. Finally, the implications of the present findings introduce a fruitful discussion in the search for effective structures to improve the piezoelectric response and represent the key point to design new domains that allow engineering the piezoelectric response.