Structural and Dielectric Properties of Titania Co-Doped with Yttrium and Niobium: Experimental Evidence and DFT Study

This work explores the impact of the sintering temperature and co-dopant contents on the microstructure and dielectric properties of (Y0.5Nb0.5)xTi1−xO2 (0.025 ≤ x ≤ 0.10) ceramics synthesized by the solid state reaction method. The physical mechanism underlying the colossal electric permittivity was systematically investigated with experimental methods and first principles calculations. All specimens exhibited the characteristic tetragonal structure of rutile, besides secondary phases. A niobium- and yttrium-rich secondary phase emerged at the grain boundaries after heating at 1500 °C, changing the main sintering mechanism. The highest value of the electric permittivity (13499 @ 60 °C and 10 kHz) was obtained for (Y0.5Nb0.5)0.05Ti0.95O2 sintered at 1480 °C, and the lowest dissipation factor (0.21@ 60 °C and 10 kHz) for (Y0.5Nb0.5)0.1Ti0.90O2 sintered at 1500 °C. The dielectric properties of Y3+ and Nb5+ co-doped TiO2 are attributed to the internal barrier layer capacitance (IBLC) and electron-pinned dipole defect (EPDD) mechanisms.