Achieving Ultralow Dielectric Loss in ZnZrNb ₂ O ₈ Ceramics via Local‐Ordering Induced by (Cr _0.5 Nb _0.5 ) ⁴⁺ Substitution: Mechanism and Application in Medical Imaging Antennas

ABSTRACT Progress in high‐sensitivity medical microwave imaging is hindered by the lack of low‐loss dielectric materials that can enable highly efficient antenna elements. Here, we propose a material design concept based on the equivalent substitution of Zr 4+ by the composite ion (Cr 0.5 Nb 0.5 ) 4+ in wolframite ZnZrNb 2 O 8 ceramics, aiming to simultaneously tailor lattice dynamics and bond characteristics to achieve ultralow intrinsic dielectric loss. A series of ZnZr 1‐ x (Cr 0.5 Nb 0.5 ) x Nb 2 O 8 (0 x 0.09) ceramics were fabricated by a solid‐state reaction route. Rietveld analysis confirms the formation of a single‐phase solid solution accompanied by systematic lattice contraction. Raman spectroscopy reveals a marked narrowing of the dominant A g mode linewidth (from 51.12 to 38.98 cm −1 ), which indicates suppressed anharmonic phonon scattering and improved local structural order. Complex chemical bond theory calculations quantitatively attribute this improvement to a progressive reinforcement of the Nb‐O bond, reflected in increased bond energy and lattice energy. As a result, at x = 0.09, the ceramic achieves a remarkable Q f value of 73,520 GHz—a 20% enhancement over the unsubstituted composition—together with a dielectric constant () of 28.31 and a temperature coefficient of resonant frequency () of −48.66 ppm/°C. To demonstrate practical relevance, a cylindrical dielectric resonator antenna was designed and simulated using the optimized composition, showing a peak gain of 4.09 dBi and a radiation efficiency exceeding 98% at 2.72 GHz. This study not only provides a high‑performance material candidate for next‑generation high‑sensitivity medical microwave imaging systems but also establishes a fundamental mechanism for reducing dielectric loss through composite‑ion substitution, offering a general design blueprint for advanced functional ceramics.