Unlocking High Dielectric Tunability and Exceptional Electrocaloric Performance via Growth‐Driven Domain Dynamics

Abstract

ABSTRACT Achieving simultaneously high dielectric tunability, thermal and frequency stability, and efficient electrocaloric performance remains a major unresolved challenge in lead‐free ferroelectric films. These constraints limit the practical deployment of environmentally benign tunable components and solid‐state refrigeration technologies. To address this gap, we investigate Ba 0 . 7 Ca 0 . 3 TiO 3 thin films grown at 630, 670, and 700°C, establishing quantitative growth–structure–property correlations that enable co‐optimization of these functionalities. By integrating dielectric spectroscopy, Rayleigh analysis, phase‐field simulations, and electrocaloric measurements, we disentangle intrinsic and extrinsic contributions governing dielectric and electrocaloric behaviour. Film grown at 630°C exhibit the highest tunability (∼90%), dominated by extrinsic mechanisms with mixture of a/c nano‐domains, whereas film grown at 670°C yields a stable tunability (∼85%), low dielectric loss (<0.05), high cumulative quality factor ( CQF ∼1.6 × 10 4 ), and excellent thermal (300–420 K) and frequency (10 kHz–1 MHz) stability. In contrast, films grown at 700°C display the best performance of electrocaloric coefficient (ξ ∼0.025 K cm kV − 1 ), refrigerant capacity ( RC of ∼1900 J kg − 1 ) and an outstanding relative cooling power (RCP ≈ 1755 K 2 ), among the highest reported for lead‐free films. These results establish growth temperature as an effective control parameter for overcoming tunability–stability trade‐offs in adaptive microelectronics and solid‐state refrigeration.