Enhanced Energy Storage Properties in Lead-Free (1−x)(BNT–5BT)–xBCZT Ceramics: Comparative Study of Direct and Indirect Synthesis Routes

This work presents a comparative study on the structural, microstructural, and functional properties of a novel lead-free solid solution based on (1−x)(0.95(Bi0.5Na0.5)TiO3–0.05BaTiO3)–x(0.5Ba0.7Ca0.3TiO3–0.5BaTi0.8Zr0.2O3), abbreviated as (1−x)(BNT–5BT)–xBCZT, with x values ranging from 0 to 0.20. Two different synthesis routes were evaluated: a direct route, where all raw materials were mixed and processed in a single step, and an indirect route, where BNT–5BT and BCZT were pre-synthesized separately and later combined. X-ray diffraction (XRD) and Raman spectroscopy confirmed the formation of single-phase perovskite structures, with progressively increasing tetragonality as x increased. Field-emission scanning electron microscopy (FE-SEM/EDS) revealed dense microstructures and secondary rod-like phases whose morphology and amount evolved with composition. Dielectric measurements indicated an enhanced relaxor behavior with increasing BCZT content, evidenced by a shift in the TF–R with frequency. The direct route resulted in more efficient dopant incorporation, leading to stronger dielectric relaxation, reduced hysteresis losses, and improved energy storage performance. The maximum energy efficiency (η) reached 43.7% for x = 0.075 via the direct route, compared to 38.0% for the same composition prepared by the indirect route. The maximum recoverable energy density (Wrec) reached 0.42 J·cm−3 for x = 0.075 via the direct route (vs. 0.40 J·cm−3 for the indirect route), with corresponding peak energy efficiencies of 43.7% and 38.0%, respectively. These findings demonstrate that (1−x)(BNT–5BT)–xBCZT ceramics synthesized via the direct route constitute a promising and scalable approach for high-efficiency, lead-free dielectric capacitors.