A systematic investigation of reliability issues in lead-free piezoelectric materials

Currently, Pb(Zr,Ti)O3 (PZT) and its derivatives are widely used in various electronic applications such as sensors, transducers, and actuators due to their superior piezoelectric properties and performance. However, there has been intense research over the past twenty years for the development of more environmentally friendly alternatives to PZT, due to the toxicity of lead (Pb) in the composition. Bi0.5Na0.5TiO3 (BNT) based lead-free piezoelectric ceramics are emerging as one of the prominent material candidates to replace PZT. In this research, it is aimed to investigate property and performance of BNT based binary (BNT-BT and BNT-BKT) and ternary (BNT-BKT-BT) solid-solutions doped with different elements. The effects of these dopants on piezoelectric (d33), dielectric (εr, tanδ, Td ve TC), and ferroelectric (Ec, Ps ve Pr) properties were investigated as well as crystal structure and microstructure. Throughout the study, 0.94(Bi0.5Na0.5TiO3)-0.06(BaTiO3) (BNBT6), 0.80(Bi0.5Na0.5TiO3)-0.20(Bi0.5K0.5TiO3) (BNKT20), and 0.854(Bi0.5Na0.5TiO3)-0.12(Bi0.5K0.5TiO3)-0.026(BaTiO3) (BNKBT12) ceramics were doped with Al3+, La3+, Mn3+, and Nb5+ ions, which were predicted to show donor and/or acceptor behavior in light of existing literature and scientific theories. For the structural characterization of the produced samples with different compositions density measurement, X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods were used. In order to systematically investigate the effects of different doping ions on the electrical properties, essential dielectric, piezoelectric and ferroelectric measurements were performed as a function of temperature, voltage, and time. For this purpose, variables were determined to optimize the "poling" conditions, which are known to play a critical role in achieving superior piezoelectric properties and performance. In addition to the measurements obtained at room temperature, temperature-dependent dielectric properties, time and temperature-dependent depolarization behavior and ferroelectric hysteresis measurements were also performed. When the results were analyzed, the findings obtained from the doping of boron (B3+) alone, as well as in combination with Al3+, La3+, Mn3+, and Nb5+ ions in BNT-BT, BNT-BKT binary, and BNT-BKT-BT ternary systems, were systematically discussed and evaluated. It was shown that boron (B2O3) doping, in addition to its well-known effect of lowering the melting point to facilitate sintering in ceramic and glass materials, also significantly improved the electrical properties by modifying the perovskite crystal structure in lead-free piezoelectric ceramics. The results observed in the studied perovskite systems, obtained by doping boron (B3+) in combination with carefully selected ions like Al3+, La3+, Mn3+, and Nb5+, allowed for a "structure-properties" evaluation from the perspective of potential point defects chemistry. The findings and evaluations obtained in this study hold the potential to make significant contributions to the scientific literature and the development of next-generation, environmentally friendly lead-free piezoelectric materials for electronic applications.