Dielectric, Ferroelectric, and Piezoelectric Performances of Poled Nb-Doped BZT-BCT Prototypes
The increasing demand for high-performance piezoelectric materials in sensors, actuators, and energy harvesters, particularly within medical and industrial domains, has long been met by lead zirconate titanate (PZT), which dominated the market for decades due to its superior electrical properties.
However, its high lead content and toxic fabrication process pose significant environmental and disposal challenges. Regulatory frameworks, such as the European Union’s Waste Electrical and Electronic Equipment directive, have accelerated the search for sustainable, lead-free alternatives.
One of the most promising alternatives is barium zirconate titanate–barium calcium titanate (BZT-BCT), a lead-free perovskite material whose piezoelectric performance can be enhanced through donor doping.
Ferroelectric domain mobility improves significantly by introducing niobium ions into the lattice, resulting in enhanced dielectric and piezoelectric responses. Poling treatments, which align ferroelectric domains under an external electric field, further amplify these properties.
Building on these principles, this research proposes niobium-doped BZT-BCT thin films as an environmentally sustainable alternative to PZT, demonstrating improved dielectric, ferroelectric, and piezoelectric properties after optimized poling treatments.
These films were fabricated via a sol–gel process using non-toxic solvents compatible with industrial MEMS fabrication. The chemical solution was carefully formulated to achieve the desired stoichiometry, resulting in the perovskite composition 0.5BaZr0.19Ti0.79Nb0.02O₃ – 0.5Ba0.7Ca0.3Ti0.98Nb0.02O₃.
Multiple spin-coating and pyrolysis cycles, followed by annealing at 750 °C, yielded 300 nm-thick films with dense, uniformly distributed nanograins and no visible cracks. Electron microscopy confirmed the absence of secondary phases, verifying the successful incorporation of niobium into the lattice.
Prototypes were fabricated with platinum top electrodes, patterned as both square capacitors and cantilever structures, allowing comprehensive evaluation of their electrical and piezoelectric performance.
Ferroelectric testing revealed stable switching characteristics across varying fields and frequencies. Higher voltages increased the coercive field as well as both residual and maximum polarization, while polarization predictably decreased at higher frequencies.
These results confirm that niobium doping enhances the ferroelectric properties of BZT-BCT while preserving its lead-free sustainability. Capacitors with smaller device sizes demonstrated higher dielectric constants due to fewer structural defects. A slight hysteresis loop asymmetry was observed, resulting from built-in electric fields generated by interfacial space charge effects.
Performance was further enhanced through optimized poling conditions, with a six-hour treatment at 60 °C under a 10 V DC bias, safely below the material’s Curie point temperature of approximately 80 °C.
Piezoelectric tests on cantilever devices using a Laser Doppler Vibrometer showed a four times increase in primary resonance displacement and the emergence of a secondary mode above 5 kHz. The cantilever achieved a 12 nm displacement at 1.84 kHz under a 3 V input, confirming the effectiveness of optimized poling in enhancing piezoelectric activity.
These results demonstrate the potential of poled niobium-doped BZT-BCT thin films as lead-free, high-performance piezoelectric materials for MEMS devices, biomedical implants, and energy-harvesting systems such as piezoelectric nanogenerators.
Future research could focus on advanced dopant engineering, improved deposition techniques for larger, uniform films, and long-term reliability under real-world conditions. While completely replacing PZT remains a challenge, this study presents a clear pathway toward environmentally responsible, high-performance piezoelectric technologies.