Experimental and theoretical investigation of the high dielectric permittivity of tantalum doped titania

Abstract

A series of tantalum doped titania samples were synthesized by a solid-state reaction method and thoroughly characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron paramagnetic resonance spectroscopy (EPR). The electrical behavior of the samples has been investigated by dielectric and impedance spectroscopy. The XRD study reveals that the pristine and doped titania crystallizes in the rutile phase. EPR studies suggest that some of the Ti⁴⁺ is reduced to Ti³⁺ attributed to doping of Ta⁵⁺ in the titania lattice. Furthermore, these materials exhibit high dielectric permittivity which may be due to the conventional inter barrier layer capacitance effect. Among the samples, the 1 mol% Ta⁵⁺ doped TiO₂ composition shows the highest dielectric permittivity. Upon increasing the amount of Ta⁵⁺, the dielectric permittivity decreases and the dielectric loss slightly increases. The dielectric permittivity of the Ta-doped TiO₂ system is found to be lower than that of the previously reported Nb-doped TiO₂ system. Based on DFT calculations it is found that the diffused nature of the 5d orbital and lower polarizability of Ta are responsible for the lower dielectric permittivity of Ta doped TiO₂ in comparison to Nb doped TiO₂ systems.