A groundbreaking advancement in lead-free piezoelectric ceramics promises to reshape the future of precision actuators, offering enhanced performance with reduced environmental impact. Researchers led by Professor Bo-Ping Zhang at the University of Science and Technology Beijing have unveiled a novel one-step sintering process for BiFeO3-BaTiO3 (BF-BT) ceramics, overcoming long-standing barriers that have hindered the practical application of these materials. This method offers a transformative approach, enabling ultra-high piezoelectric properties, improved stability, and reproducibility, heralding a new era for high-temperature piezoelectric devices.
Piezoelectric materials convert mechanical stress to electrical charge and vice versa, underpinning technologies such as sensors, actuators, and precision displacement devices. Traditionally, lead-based ceramics like Pb(Zr,Ti)O3 (PZT) have dominated due to their exceptional electromechanical properties. However, the drive for environmentally friendly alternatives necessitates the replacement of lead-based compounds with lead-free solutions. Among these candidates, the BF-BT system attracts interest because of its high Curie temperature and robust ferroelectricity. Despite these advantages, practical deployment has been impeded by significant issues: high leakage currents, poor reproducibility, and the formation of deleterious secondary phases.
The core challenge arises from the thermodynamic instability of BiFeO3 within the temperature range of approximately 447 °C to 767 °C. This instability promotes the emergence of secondary non-ferroelectric phases during conventional multi-step solid-state sintering, accompanied by bismuth volatilization and the generation of oxygen vacancies. Such defects compromise the material’s electrical properties and reliability. Addressing this complex interplay of defects and phase stability demands an innovative fabrication approach that can circumvent the problematic thermal window effectively.
In this context, the breakthrough comes with the development of a one-step sintering methodology that integrates binder removal, pre-sintering, and sintering into a single heat treatment process. Diverging from the traditional multi-step reaction routes, this technique initiates material synthesis directly starting from BaTiO3 and BiFeO3 precursors, thus avoiding the unstable phase transition window where BiFeO3 decomposition and volatility issues are most pronounced. By consolidating the thermal treatments, the process effectively suppresses the formation of impurity phases and substantially widens the permissible processing conditions.
This innovation simplifies the fabrication process while simultaneously enhancing the ceramic’s electrical and mechanical characteristics. The tighter control over phase purity and microstructural homogeneity achieved via the one-step process dramatically increases reproducibility. Prof. Zhang emphasizes that this streamlined approach not only boosts fabrication efficiency but also unlocks superior comprehensive performances previously unattainable with BF-BT ceramics. This advancement addresses a critical bottleneck, enabling the development of high-performance devices with environmentally sustainable lead-free materials.
Moreover, the research team explored the influence of iron non-stoichiometry in the BF-BT system by fabricating a series of 0.7BiFe1+xO3–0.3BaTiO3 ceramics, where x ranges from -0.05 to +0.05. This deliberate modulation of Fe content magnifies defect chemistry effects, permitting a systematic study of defect evolution and its macroscopic influence on material properties. Their findings underline the complex interplay between vacancies, defect dipoles, and charge carriers that govern electrical behavior and piezoelectric performance.
Detailed electrical testing revealed that, at room temperature, holes constitute the primary charge carriers, their concentration directly linked to oxygen vacancy density. Contrastingly, at elevated temperatures beyond 300 °C, oxygen vacancies themselves become dominant conduction carriers. Critically, the pinning of these vacancies by defect dipoles controls leakage current magnitudes. Such insights into the fundamental mechanisms of leakage conduction provide essential guidelines for defect engineering, enabling precise tailoring of electrical properties to minimize losses and enhance device longevity.
Beyond electrical characteristics, the study also delved into strain behavior—an essential factor for piezoelectric actuation. Prior to poling, samples exhibited variable degrees of bipolar strain asymmetry contingent on Fe non-stoichiometry. Notably, a composition with x = -0.05 demonstrated pronounced strain asymmetry, which diminished incrementally with increased Fe content. Post-poling measurements revealed that all ceramics exhibited bipolar strain asymmetry but followed a different trend. The poling process induces redistribution of space charges at grain boundaries, generating additional internal bias fields that modulate ferroelectric switching dynamics. This dual regulation effect enables tuning of the strain response, allowing customized performance profiles for specific applications.
Perhaps most striking is the outstanding combination of electromechanical properties realized by the novel ceramics. The optimized 0.7BF-0.3BT ceramic attains a piezoelectric coefficient (d33) of 201 pC/N and a Curie temperature (Tc) soaring to 501 °C. These values surpass those typically reported for BF-BT systems and outperform alternative lead-free families such as potassium sodium niobate (KNN)-based and bismuth sodium titanate (BNT)-based ceramics. Additionally, the high-field piezoelectric coefficient d33* reaches an impressive 1021 pm/V, accompanied by a substantial room-temperature strain of 0.38%. This synergy of high piezoelectric response, thermal stability, and mechanical strain exemplifies the ceramic’s suitability for demanding actuator applications, especially under high-temperature conditions.
The robustness of the one-step sintering approach further manifests in its tolerance to Fe stoichiometric variations. Consistent performance metrics across a wide range of compositions confirm that the method can reliably produce high-quality materials with stable piezoelectric outputs, a critical factor for scalable manufacturing and industrial adoption. This resilience underscores the technique’s potential to establish new standards in lead-free piezoelectric ceramic preparation.
The implications of this research resonate across sectors reliant on precision actuation and sensing under challenging environmental conditions. High-temperature actuators with environmentally benign compositions are imperative for advancing green technologies in aerospace, automotive, industrial automation, and energy harvesting systems. By delivering a lead-free ceramic exhibiting unprecedented piezoelectric and thermal properties, this study paves the way for practical, eco-friendly replacements to traditional lead-based materials, harmonizing performance with sustainability.
Beyond experimental breakthroughs, the work contributes fundamental knowledge on defect management in complex oxide ceramics. The elucidation of defect dipole formation, space charge dynamics, and their coupling to ferroelectric switching enriches the theoretical framework guiding next-generation material design. Researchers in piezoceramics and ferroelectrics can leverage these insights to further optimize material systems, extending the impact of this novel processing technique.
Professor Bo-Ping Zhang’s team at USTB has thus delivered a landmark advancement in materials science, demonstrating that strategic integration of materials chemistry with innovative processing can unravel longstanding challenges. Their one-step sintering process transforms the landscape of lead-free piezoelectrics, setting the stage for future research and commercialization focused on high-performance, sustainable actuator technologies aligned with global environmental goals.
Subject of Research: Lead-free piezoelectric ceramics; BiFeO3-BaTiO3 system; defect engineering; one-step sintering process; high-temperature actuators
Article Title: Ultra-high piezoelectric properties of BiFeO3–BaTiO3 lead-free piezoelectric ceramics enabled by a one-step sintering process
News Publication Date: April 21, 2026
Web References:
Journal of Advanced Ceramics
DOI:10.26599/JAC.2026.9221302
Image Credits: Journal of Advanced Ceramics, Tsinghua University Press
Keywords
Lead-free piezoelectrics, BiFeO3-BaTiO3 ceramics, one-step sintering, defect dipoles, high Curie temperature, piezoelectric coefficient, oxygen vacancies, ferroelectric switching, high-temperature actuators, environmental sustainability, fabrication innovation, defect engineering
