Low‐Field Giant Dielectric Tunability by Polaron‐Mediated Interfacial Polarization in Pulsed‐Laser‐Deposited‐Nanocrystalline/Amorphous Composite BaTiO ₃ Thin Films

Electrically tunable dielectric thin films are essential components for next‐generation low‐voltage electronic devices. This is difficult to achieve with conventional ferroelectrics, which typically require high driving fields and often exhibit substantial dielectric loss and leakage currents. Here, we report exceptional low‐field dielectric tunability efficiency in BaTiO 3 (BTO) thin films grown by pulsed laser deposition (PLD) under vacuum conditions. The PLD‐BTO films deposited at an intermediate temperature ( T d ) of 550°C exhibit a colossal dielectric constant exceeding 3000 with a loss tangent as low as 0.04, together with a maximum tunability efficiency ( η ) of 1.28, significantly surpassing previously reported lead‐free and lead‐based tunable dielectric films. Structural characterization reveals the formation of a self‐organized nanocrystalline/amorphous homo‐composite architecture, while X‐ray photoelectron spectroscopy confirms oxygen‐vacancy‐induced Ti 3 + polaron generation. These mobile polarons give rise to giant Maxwell–Wagner‐type interfacial polarization, enabling pronounced dielectric tunability under low DC bias fields. Post‐annealing in oxygen suppresses Ti 3 + states and eliminates the tunable response, thereby highlighting the critical role of oxygen‐related defects and polaron‐mediated interfacial polarization in enhancing dielectric functionality. This work establishes a scalable defect‐ and nanostructure‐engineering strategy for designing high‐efficiency, low‐voltage tunable dielectrics beyond conventional ferroelectric approaches, with strong potential for energy‐efficient electronic and thermal switching applications.