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° domain templates are resolved by 60° and 120° domains. The internal stress results in the appearance of an unusual polarization relaxation at the 90° 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.

The present article aims to give a brief overview about the advantages of the hydrothermal crystallization method for the synthesis of advanced ceramics. Emphasis is given, not only on the conventional hydrothermal crystallization, but also on some of its variants; such as ultrasound-assisted, electrochemical-assisted, microwave-assisted and surfactant-assisted hydrothermal methods which open up new opportunities for the synthesis of ceramic materials with novel properties demanded for advanced applications. In the current work the synthesis of barium titanate (BaTiO₃), lithium metasilicate (Li₂SiO₃) and sodium-potassium niobate (Na, K)NbO₃ powders are reported as cases of study.