Breaking the Tunability–Loss Trade‐off in Bi ₆ Ti ₅ WO ₂₂ ‐Based Relaxors via Nominal Compositional Tuning

ABSTRACT Achieving high dielectric tunability with minimal dissipation remains a critical challenge for next‐generation microwave devices and is often elusive in conventional perovskites due to intrinsic losses. Here, we investigate a non‐perovskite Bi 6 Ti 5 WO 22 (BTWO)‐based relaxor system synthesized via a sol–gel route. Unlike conventional solid‐state methods, this approach ensures superior precursor homogeneity, enabling controlled access to a narrow phase stability window. We demonstrate that precisely targeting the optimal BTWO‐49Bi composition eliminates detrimental secondary phases while simultaneously minimizing local lattice disparity. Consequently, the optimized ceramics deliver a high figure‐of‐merit (FOM ≈ 1500), characterized by a large tunability (60% at 30 kV cm −1 ) and an ultralow dielectric loss (tan δ in the ∼ 10 −4 range). By correlating macroscopic electrical responses with local structural probes, we reveal that this enhanced microscopic uniformity effectively minimizes random pinning fields. As a result, the intrinsic polar nanoregions (PNRs) retain high rotational freedom and respond to external fields highly cooperatively. Ultimately, this work breaks the conventional tunability‐loss trade‐off, confirming an effective strategy to explore the intrinsic structural limits of the BTWO system.