Electrocaloric and energy storage properties of lead-free Na0.5Bi0.5Ti0.6Hf0.4O3 ferroelectric ceramics for sustainable energy solutions are affected by the sintering temperatures

Ferroelectric materials are widely regarded as promising candidates for sustainable energy technologies, particularly in solid-state cooling and energy-storage applications. In this work, the microstructural, dielectric, electrocaloric, and energy-storage properties of sol–gel-derived Na _0.5 Bi _0.5 Hf _0.4 Ti _0.6 O ₃ (NBHT) ceramics were systematically investigated. X-ray diffraction (XRD) analysis confirmed the coexistence of monoclinic and tetragonal phases, with an enhanced tetragonal contribution observed at higher sintering temperatures. Increasing the sintering temperature facilitated grain growth, improved densification, and significantly enhanced the dielectric and ferroelectric responses. The NBHT ceramic sintered at 1100 °C exhibited a maximum electrocaloric temperature change (ΔT) of 0.35 K and a recoverable energy density (W _rec ) of 1.52 J cm ^-3 with an energy efficiency of approximately 80% at 120 °C. In contrast, the sample sintered at 1200 °C demonstrated a W _rec of 1.02 J cm ^-3 and high efficiency of 79.13% under an applied electric field of 40 kV cm ^-1 . These findings reveal that the NBHT ceramics exhibit a strong electrocaloric effect coupled with excellent energy-storage performance, underscoring their potential as lead-free ferroelectric materials for next-generation solid-state cooling and energy-storage devices.