A lead-free Ba0.85Ca0.15Ti0.9Zr0.1O3 ferroelectric ceramic with tailored microstructure and ultrahigh piezo-strain response
AMORÍN H. 1, VENET M. 2, GARCÍA J. 3, OCHOA D. 3, RAMOS P. 4, CASTRO A. 1, ALGUERÓ M. 1
1 Instituto de Ciencia de Materiales de Madrid - CSIC, Madrid, Spain; 2 Departamento de Física, Universidade Federal de São Carlos, São Carlos, SP, Brazil; 3 Department of Physics, Universitat Politecnica de Catalunya, Barcelona, Spain; 4 Departamento de Electrónica, Universidad de Alcalá, Alcalá de Henares, Spain
The growing environmental concerns, along with the necessity of adapting the piezoelectric technologies to the currently enforced EU-Directive 2002/95/EC (RoHS), have driven the piezoceramic materials industry to develop ecologically-friendly alternatives to current-state-of-the-art Pb(Zr,Ti)O3 (PZT) commercial ceramics. Besides, health concerns related to lead toxicity hinder their potential use as active biomedical implants, where piezoelectric materials can interact with bones and cells through electrical signals. Ferroelectric perovskites based on Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3 have emerged as leading candidates to replace PZT, due to its high piezoelectric coefficients. However, one important limitation in the transfer of BCZT to current piezoelectric technologies is the still challenging ceramic processing that requires very high temperatures that normally results in abnormal grain growth and brittle microstructures that compromise reliability.
In this context, we have combined advanced synthesis and sintering techniques to obtain high-quality BCZT ceramics with tailored microstructures and controlled sub-10 µm grain growth, that is, spark plasma sintering (SPS) of nanocrystalline powders obtained by mechanosynthesis. The effect of the processing parameters in obtaining coarse- or fine-grained microstructures, and in turn on the dielectric, ferroelectric and piezoelectric properties is discussed. Fine-grained sub-10 µm sized material showed very high strain under the electric field of about 2000 pm V-1, a value significantly higher than those typically reported for lead-free ceramics. High-energy, synchrotron radiation was used to study the mechanisms behind the ultra-high piezo-strain response, in order to elucidate among the extrinsic domain wall motion contributions and the intrinsic ones, related to the electric-field induced phase transformations between coexisting polymorphs at the MPB.
Acknowledgments: Funded by Spanish MINECO Project PID2021-122708OB-C33. Technical support of Ms. Inmaculada Martínez, at ICMM-CSIC, is also acknowledged.