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

Abstract

Abstract 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 x Ta2.5%Ti0.975−x O2 (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.

Keywords

• TiO2
• Giant/Colossal permittivity
• Co–dopant
• Grain boundary
• Interfacial polarization