A guiding framework for giant dielectric mechanisms in antimony(V)/yttrium(III) co‒doped TiO2: defect‒cluster polarization, IBLC, and interface effects

• Y/Sb co-doped TiO 2 shows low tanδ and high ε′ with high stability. • Defect-cluster polarization dominates, while EPDD formation is excluded by DFT. • Synergistic roles of Y 3+ -induced vacancies and Sb 5+ -donated electrons clarified • Robust dielectric mechanisms verified across wide temperature and frequency ranges. • IBLC and Schottky effects correlated with impedance and I–V characteristics. Understanding and engineering colossal permittivity in rutile TiO 2 remains challenging, particularly under the combined constraints of low dielectric loss and temperature stability. Here we investigate (Y 0.5 Sb 0.5 ) x Ti 1- x O 2 ceramics with x = 0.5%–15% prepared by a conventional solid–state route to clarify the origin of the response and identify practical compositions. Structural and microstructural characteristics were examined by X–ray diffraction with Rietveld refinement, Raman spectroscopy, SEM–EDS, and XPS, while dielectric behavior was evaluated by broadband measurements from 15 to 483 K together with impedance spectroscopy using electrode and thickness controls. The 0.5%YSbTO composition delivers a relative permittivity ε′∼7.2 × 10 4 with tanδ ∼ 0.017 at 1 kHz and room temperature, and maintains |Δε′/ε′ RT | ≤ ±15% from 213 to 483 K, consistent with X7R to X9R temperature stability. Three thermally activated relaxations are resolved (R1–R3). Arrhenius analysis yields activation energies of 0.014–0.029 eV for R1, 0.169–0.285 eV for R2, and 0.116–0.123 eV for R3. R1 appears at low temperatures and is attributed to intrinsic polarization associated with complex defect dipoles formed by Y 3+ /Sb 5+ –induced defect complexes, as supported by first–principles DFT calculations. R2 emerges at intermediate to high temperatures and is attributed to interfacial polarization associated with an internal barrier layer capacitor (IBLC) structure at semiconducting grain/insulating grain-boundary interfaces. R3 dominates at higher temperatures and arises from Schottky–type polarization at the sample–electrode interface. These results link defect chemistry and interfacial polarization to temperature–stable, low–loss colossal permittivity in co–doped TiO 2 , and identify 0.5%YSbTO as a promising dielectric for reliable capacitor applications.