Koruza, Jurij ; Rojas, Virginia ; Molina-Luna, Leopoldo ; Kunz, Ulrike ; Dürrschnabel, Michael ; Kleebe, Hans-Joachim ; Acosta, Matias (2016)
Formation of the core–shell microstructure in lead-free Bi1/2Na1/2TiO3-SrTiO3 piezoceramics and its influence on the electromechanical properties.
In: Journal of the European Ceramic Society, 36 (4)
doi: 10.1016/j.jeurceramsoc.2015.11.046
Article, Bibliographie

Abstract

The Bi 1/2Na1/2TiO3-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 Bi 1/2Na1/2TiO3-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%.

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