- The paper shows that incorporating BaHfO3 (optimal at x=0.1) into NaNbO3 thin films improves breakdown strength up to 1112.1 kV/cm and refines microstructure.
- Methodology involves sol-gel synthesis, XRD and AFM characterization, and electrical measurements such as P-E hysteresis loops and Weibull analysis.
- The optimized films achieve a recoverable energy density of 23.1 J/cm³ with 66.2% efficiency, excellent thermal stability, and a rapid charge-discharge time of 0.82 µs.
Key Concepts and Experimental Setup
The paper of lead-free dielectric materials has gained importance due to environmental concerns associated with lead-based components. This paper focuses on the structural, electrical, and energy storage properties of lead-free NaNbO3-BaHfO3 (NNO-BHO) thin films. Thin films with a composition (1-x)NaNbO3-xBaHfO3 for x ≤ 0.15 were prepared using a sol-gel method. The addition of BaHfO3 (BHO) aims to enhance the dielectric and energy storage capabilities by stabilizing the antiferroelectric (AFE) characteristics and increasing the breakdown strength.
The films were fabricated on Nb-doped SrTiO3 substrates, utilizing a sol-gel process. The structural and morphological characteristics were analyzed using X-ray diffraction (XRD) and atomic force microscopy (AFM). Electrical properties including P-E hysteresis loops and leakage current were measured using capacitors formed by sputtering Au electrodes on the films. The capacity for energy storage was assessed through the calculation of the energy storage density and efficiency from P-E loops.
Structural and Morphological Analysis
XRD patterns confirmed the perovskite structure with highly oriented growth along the (001) direction for all examined films. Incremental BHO composition led to lattice expansion, as indicated by the shift in diffraction peaks. BHO's effect was significantly manifested through a denser microstructure and reduced grain sizes, confirmed by AFM analysis. The RMS roughness values revealed consistent refinement with BHO incorporation, pivotal for improving breakdown strength.
Electrical Properties and Energy Storage
The paper reported significant reductions in leakage current density with BHO doping. Undoped films exhibited high leakage, attributed to volatile sodium ions forming cation vacancies and oxygen defects. The introduction of BHO improved the films' conductivity, likely due to enhanced microstructural factors and defect minimization.
Frequency-dependent studies of dielectric constants displayed typical relaxation behavior with a moderate decrease at higher frequencies. The space-charge polarization, as a characteristic at high frequencies, was noted as an influencing factor. Furthermore, dielectric loss was observed to decrease with the increase of BHO content, essential for the films' energy storage efficacy.
The Weibull analysis revealed significant enhancement in breakdown strengths upon BHO incorporation, reaching up to 1112.1 kV/cm at x=0.1. This enhancement corroborates with the films' improved structural homogeneity and lower defect densities. For energy storage, the optimal composition (x=0.1) achieved a high recoverable energy density of 23.1 J/cm³ at 1100 kV/cm with an efficiency of 66.2%, comparable to reported values for NaNbO3-based thin films.
Thermal Stability, Fatigue Resistance, and Fast Charge-Discharge
The x=0.1 films demonstrated excellent thermal stability over a temperature range of 30 to 210°C and showed minimal performance degradation after cycling (less than 2.9% loss after 10,000 cycles). Fast charge-discharge characteristics were evidenced by a discharge time of 0.82 µs at various applied fields, underlining the films' applicability in rapidly discharging electronic devices.
Conclusion
This investigation into NNO-BHO thin films demonstrates their potential as viable lead-free dielectric materials for energy storage. The inclusion of BaHfO3 significantly enhances microstructure, electrical characteristics, and energy storage performance, particularly at x=0.1. Their thermal stability, fatigue resistance, and rapid discharge capabilities position these materials as promising candidates for incorporation into microelectronic devices, aligning with environmental initiatives to phase out lead-based technologies. Future endeavors may explore broader compositional variations and long-term stability assessments to further optimize these materials.