Electrocaloric effect and high energy storage efficiency in lead-free Ba$_{0.95}$Ca$_{0.05}$Ti$_{0.89}$Sn$_{0.11}$O$_3$ ceramic elaborated by sol-gel method

Abstract: Structural, dielectric, ferroelectric, energy storage properties, and electrocaloric effect were studied in lead-free ceramic Ba${0.95}$Ca${0.05}$Ti${0.89}$Sn${0.11}$O$_3$ (BCTSn) elaborated by sol-gel method. Phase purity structure was confirmed from X-ray data using Rietveld refinement analysis which revealed the coexistence of tetragonal (P4mm) and orthorhombic (Amm2) symmetries at room temperature. Phase transitions were detected by dielectric and differential scanning calorimetry results. Energy storage properties were determined from P-E hysteresis, and the electrocaloric properties were calculated indirectly via the Maxwell approach. The large value of electrocaloric temperature change of $\Delta$T=0.807 K obtained at a relatively small field of 30 kV cm$^{-1}$ and high energy storage efficiency can make BCTSn ceramic a promising candidate for environmentally friendly refrigeration and energy storage applications.

• The paper demonstrates a high energy storage efficiency of 91.07% at 373 K and a notable electrocaloric temperature change of 0.807 K in BCTSn ceramics.
• It employs techniques like XRD with Rietveld refinement, DSC, dielectric measurements, and P-E hysteresis loops to characterize phase coexistence and ferroelectric performance.
• Results show that Ca and Sn doping stabilize the morphotropic phase boundary, enhancing the dielectric constant (up to 11,979) and boosting energy density to 124 mJ/cm³.

Electrocaloric Effect and High Energy Storage Efficiency in Ba$_{0.95}$Ca$_{0.05}$Ti$_{0.89}$Sn$_{0.11}$O$_3$ Ceramic

Introduction

The paper explores the electrocaloric effect (ECE) and energy storage efficiency in the lead-free Ba$_{0.95}$Ca$_{0.05}$Ti$_{0.89}$Sn$_{0.11}$O$_3$ (BCTSn) ceramic, synthesized using the sol-gel method. The BCTSn ceramic system presents a promising alternative to traditional Pb-based materials due to its environmentally friendly nature and potential for use in solid-state cooling and energy storage applications. The research highlights the material's structural, dielectric, ferroelectric, and electrocaloric properties, emphasizing its large temperature change under a relatively small electric field and high energy storage efficiency.

Materials and Methods

The study employs Rietveld refinement on X-ray diffraction (XRD) data to confirm the phase purity and the presence of mixed tetragonal and orthorhombic phases in BCTSn ceramics. Differential scanning calorimetry (DSC) and dielectric measurements identify phase transitions, while P-E hysteresis loops are used to extract ferroelectric and energy storage characteristics. The electrocaloric properties are evaluated using the indirect Maxwell approach, typical for these investigations. The sol-gel synthesis technique, chosen for its ability to promote compositional homogeneity and reduce calcination temperatures, plays a crucial role in maximizing the ceramic's performance.

Results and Discussion

Structural and Dielectric Properties

The XRD analysis confirms the coexistence of tetragonal and orthorhombic phases in the BCTSn ceramic. The dielectric measurements reveal phase transitions at temperatures corresponding to R-O, O-T, and T-C transitions, significantly enhanced compared to the basic BaTiO$_3$ system due to Ca and Sn doping. The substitution of Sn for Ti and Ca for Ba aids in stabilizing the morphotropic phase boundary (MPB), crucial for the observed enhancements. The BCTSn ceramic demonstrates a maximal dielectric constant of about 11,979 at 1 kHz, indicating higher dielectric performance than other formulations.

Ferroelectric and Energy Storage Properties

Ferroelectric characterization through P-E loops shows well-saturated hysteresis, crucial for energy storage applications. Maximal polarization ($P_{\text{max}}$), remnant polarization ($P_r$), and coercive field ($E_c$) show typical thermal dependence, with BCTSn achieving energy storage efficiency ($n$) up to 91.07% at 373 K and an energy density of 124 mJ/cm$^3$. Comparisons with literature highlight the superior performance of BCTSn ceramics, attributed to enhanced material synthesis and optimized phase coexistence.

Electrocaloric Effect

The ECE of BCTSn, characterized by a temperature change ($\Delta T$) of 0.807 K and electrocaloric responsivity ($\Delta S$) of 0.268 K mm/kV at 30 kV/cm, underscores its efficiency, surpassing similar lead-free systems. These properties are exploited near the MPB, leveraging phase transitions for maximal entropy and temperature changes. The BCTSn system's high coefficient of performance (COP) of 8.8 further validates its potential in eco-friendly refrigeration technologies.

Conclusion

The BCTSn ceramic exhibits promising electrocaloric and energy storage properties due to its unique composition and optimized synthesis pathway. The advancement towards environmentally friendly and efficient energy storage solutions sets the stage for its application in next-generation cooling technologies and high-density energy storage systems. Future research directions may focus on optimizing compositional variants and exploring synthesis alternatives to further enhance its operational efficiency and application range.