his work was partially supported by the Spanish MINECO R&D Project with ref. MAT-2017-86168R. The scholarship of A. Iacomini and M. Mureddu was supported by a joint agreement between Universities of Sassari and Cagliari (Italy) within the activities of the PhD programme in Chemical and Technological Sciences. The period spent by A. I. at the ICMM laboratories under the supervision of L. Pardo was made possible thanks to a generous support of the Erasmus+ programme. The authors are gratefully to Mireya Elisabet Pedrero, for her support in the toxicological assays. One of us, i.e. E. P., wishes to thank the Italian Ministry of Research for the project AIM 1815402-1 in the framework of PON R&I 2014–2020 – AIM (Attraction and International Mobility) where her activity is being performed. Fondazione di Sardegna is gratefully acknowledged for funding through “Bando Fondazione di Sardegna" 2022 e 2023 – Progetti di ricerca di base dipartimentali. All authors acknowledge the CeSAR (Centro Servizi d’Ateneo per la Ricerca) of the University of Sassari for the X-ray diffraction and SEM investigations.

In this work, “lead free” 0.99K0.5Na0.5NbO3-0.01BiFeO3 (KNN–BF) piezoceramics were prepared by a combination of mechanochemical activation, Spark Plasma Sintering and post-annealing treatment. Results show that the annealing treatment causes important microstructural and electrical changes. The SPS sample was characterized by low electrical resistance, while the air annealed samples showed better insulating properties due to a partial compensation of the oxygen vacancy. The best piezoelectric properties were found for the samples annealed at 1000 and 1050 ​°C for 2h due to the optimum grain size and oxygen vacancy compensation achieved. A further enhancement of the dielectric and piezoelectric properties was achieved through a second annealing treatment in oxygen flux at 1050 ​°C for 30 ​min. Moreover, the toxicity of the pellets was evaluated through exposure experiments to the pulverized KNN–BF pellets, employing two widely used human and environmental cellular models. © 2022 Elsevier Inc.

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