Quasi-intrinsic colossal permittivity in Nb and In co-doped rutile TiO₂ nanoceramics synthesized through a oxalate chemical-solution route combined with spark plasma sintering

Nb and In co-doped rutile TiO₂ nanoceramics (n-NITO) were successfully synthesized through a chemical-solution route combined with a low temperature spark plasma sintering (SPS) technique. The particle morphology and the microstructure of n-NITO compounds were nanometric in size. Various techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG)/differential thermal analysis (DTA), Fourier transform infrared (FTIR), and Raman spectroscopy were used for the structural and compositional characterization of the synthesized compound. The results indicated that the as-synthesized n-NITO oxalate as well as sintered ceramic have a co-doped single phase of titanyl oxalate and rutile TiO₂, respectively. Broadband impedance spectroscopy revealed that novel colossal permittivity (CP) was achieved in n-NITO ceramics exhibiting excellent temperature-frequency stable CP (up to 10⁴) as well as low dielectric loss (∼5%). Most importantly, detailed impedance data analyses of n-NITO compared to microcrystalline NITO (μ-NITO) demonstrated that the origin of CP in NITO bulk nanoceramics might be related with the pinned electrons in defect clusters and not to extrinsic interfacial effects.