Formation of the core–shell microstructure in lead-free Bi1/2Na1/2TiO3-SrTiO3 piezoceramics and its influence on the electromechanical properties

• Published in: Journal of the European Ceramic Society 2016-03, Vol.36 (4), p.1009-1016
• Main Authors: Koruza, Jurij, Rojas, Virginia, Molina-Luna, Leopoldo, Kunz, Ulrike, Duerrschnabel, Michael, Kleebe, Hans-Joachim, Acosta, Matias
• Format: Article
• Language: English
• Subjects: Core–shell; Electromechanical properties; Lead-free; Piezoelectricity; Relaxor
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2015.11.046

The Bi1/2Na1/2TiO3-based materials exhibit the largest electric-field-induced strains among lead-free piezoceramics and are considered as promising candidates for actuation applications. A typical representative of this group is (1-x)Bi1/2Na1/2TiO3-xSrTiO3, where its excellent electromechanical properties were recently related to the existence of a core–shell microstructure. Although the latter was also reported in other Bi1/2Na1/2TiO3-based ceramics, the formation mechanism remains unknown. In the present work we therefore first investigated the solid-state reaction occurring during calcination using simultaneous thermogravimetric analysis, X-ray diffraction, scanning and transmission electron microscopy. The reaction occurred in two steps, whereby the cores and shells had different formation reaction temperatures, which resulted in a metastable heterogeneous microstructure. Furthermore, a series of sintered samples with different relative densities, grain sizes, and core densities was prepared. Modifications of these microstructural parameters resulted in variation of the maximal strain by 17% and in the electric-field required to trigger the phase transitions by 38%.