Achieving Ultralow Dielectric Loss in ZnZrNb ₂ O ₈ Ceramics via Local‐Ordering Induced by (Cr _0.5

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.