Sk. Anirban

Vacancy mediated ionic conduction in Dy substituted nanoceria: a structure–property correlation study

The oxygen vacancy evolution and ion dynamics in Dy doped nanoceria have been investigated with microstructural, optical and ionic conductivity studies. The influence of Dy3+ ions on the microstructures and the optical and ionic conductivity properties of these nanoparticles has been studied using X-ray diffraction, HR-TEM, EDAX, UV-vis, Raman and impedance spectroscopy. From Rietveld refinement of the XRD profiles, it has been found that the oxygen vacancies, lattice parameters and Ce–O bond lengths increase with Dy3+ ion concentration. The Rietveld analysis, together with HR-TEM, confirms the cubic fluorite structure with space group Fmm of all the samples. The EDAX spectra show good stoichiometry of the different atoms in the samples. The direct band gap, calculated from UV-vis spectra, shows a red shift with increasing concentration of Dy3+ ions. Raman spectroscopy studies of the samples gave insight into their vibrational properties and pointed to the fact that the oxygen vacancy content increased significantly with the doping concentration. The number of oxygen vacancies and their interaction with dopant cations strongly influence the electrical properties of Dy doped ceria.

Charge carrier dynamics in Gd–Y co-doped nanocrystalline ceria corroborated with defect interactions

Defect associates and their interactions with charge carriers, influencing the ion dynamics have been discussed for Gd3+ and Y3+ co-doped nanocrystalline ceria. Detailed Rietveld analysis of the X-Ray Diffraction data confirmed the single phase cubic fluorite structure of the compositions with the space group Fmm. An overall increase of the lattice parameter with Gd3+ ion concentration has been found. Grain and specific grain boundary conductivity have been evaluated from the complex impedance plots. A higher value dielectric constant has been observed for a co-doped sample at 20 mol% doping concentration. The interaction between dopant cations with oxygen vacancies has been found to form different defect associates and defect clusters. The association energy of co-doped samples at a 20 mol% doping concentration is observed to be a minimum in comparison with the singly doped samples of the same concentration. It has also been found that different defect clusters have a significant role on ionic conduction. The correlation among structural parameters, dielectric and conductivity responses has been discussed and established.

Dielectric relaxation and charge carrier mechanism in nanocrystalline Ce–Dy ionic conductors

Ion dynamics in pure and Dy containing nanoceria has been investigated in the light of different defect associates and their mutual interactions. The samples were prepared through citrate–nitrate auto-ignition method and their single-phase cubic fluorite structure was confirmed from X-ray diffraction and high resolution transmission electron microscopy analysis. The complex impedance spectra showed both grain and grain boundary contribution to total conductivity. The concentration dependent conductivity variation has been discussed with the help of oxygen vacancy concentration and their interactions with the defect associates. The frequency dependence of dielectric permittivity and electric modulus has been analyzed using Havriliak–Negami formalism. The relaxation mechanism is found to be dependent on the formation of different dimers and trimers. Modulus analysis has established the charge re-orientation relaxation of the defects associates. The time–temperature superposition principle has been established by scaling of different spectra.

Synthesis and electrical transport properties of Gd doped nanocrystalline ceria

In this paper we report synthesis and electrical properties of Ce1−xGdxO2−δ (x=0.05−0.2) materials. The materials were prepared using the citrate auto ignition method. The XRD patterns indicate the single phase of the prepared materials. The electrical properties were studied using impedance spectroscopy in a temperature range 250°C to 550°C. It has been observed that the total ionic conductivity increases with the increase in Gd concentration. The electrical data analysis was done using the conductivity formalism.