Mechanisms of enhanced performance in Zr⁴⁺/Ta⁵⁺ codoped rutile–TiO₂ ceramics via broadband dielectric spectroscopy

Aliovalent dopant codoped rutile–TiO₂ materials have garnered attention due to their excellent performance properties, characterized by low loss tangent (tanδ), high dielectric permittivity (ε′), and stable ε′ over a broad temperature range. This performance is primarily due to the electron−pinned defect−dipoles (EPDDs) of the complex defects \(A_{2}^{{3+}}{\text{V}}_{{\text{O}}}^{{ \cdot \cdot }}\) Ti³⁺– \({\text{Nb}}_{2}^{{5+}}\) Ti³⁺B_Ti. Notably, the excellent dielectric properties in Zr_xTa_2.5%Ti_0.975−xO₂ (Zr–TTO) ceramics can be achieved using the traditional mixed oxide method without the EPDDs, due to the absence of A³⁺ (acceptor doping ions). Instead, the existence of localized free electrons and oxygen vacancies ( \({\text{V}}_{{\text{O}}}^{{ \cdot \cdot }}\) ) in Zr–TTO structures, due to doping ions and the sintering process, was confirmed by X–ray photoelectron and Raman spectroscopies. These ceramics exhibited ε′~ 2 × 10⁴ and tanδ < 0.03 at 1 kHz and 25 °C in the 2.5–10%Zr–TTO samples. Moreover, all ceramics demonstrated a maximum ε′ change (∆ε′) of less than ±15% over the temperature range suitable for X7R and X8R type ceramic capacitors. Significantly, the change in ε′ related to relative humility was calculated to be less than ±0.5% over the range of 50–95% RH, indicating the environmental stability of the dielectric properties, which is essential for capacitor applications. Investigations suggested that at least four mechanisms contributed to this system: the intrinsic effect of ionic polarization, Ti⁴⁺ · e^– – \({\text{V}}_{{\text{O}}}^{{ \cdot \cdot }}\) – Ti⁴⁺ · e^– and Ti⁴⁺ · e^– – \({\text{Ta}}_{{{\text{Ti}}}}^{ \cdot }\) defects, interfacial polarization at insulating grain boundaries, and non–Ohmic contact between the surface sample and the metal electrode.