Emergent polar order from interlayer microstrain in layered perovskites.

Ferroelectric materials with switchable polarization and nonlinear dielectric responses are promising candidates for reconfigurable communication systems. However, their practical use is limited by an inherent trade-off: large dielectric tunability is usually accompanied by high dielectric permittivity and increased loss. Layered perovskite oxides such as Sr2Ta2O7 exhibit intrinsically low dielectric permittivity and low loss, but their centrosymmetric structure limits tunability. Here, we introduce subtle interlayer microstrain in (CaxSr1-x)2Ta2O7 via site-selective Ca substitution. The resulting microstrain gradients and asymmetric distortions of neighboring TaO6 octahedra break local inversion symmetry and induce dynamic polar nanoclusters within an otherwise nonpolar matrix. This configuration enables strong tunability while maintaining low dielectric permittivity and minimal loss across the broadband spectrum. The x = 0.08 composition shows optimal performance and enables agile frequency tuning in prototype antenna systems under applied electric fields or thermal stimulus. These findings establish interlayer microstrain engineering as a paradigm for designing high-performance, lead-free tunable microwave dielectrics for adaptive communication technologies.