A. Dutta

Microstructure and charge carrier dynamics in Dy substituted phase stabilized cubic Bi2O3

Room temperature phase stabilization of cubic Bi2O3 has been achieved by adding Dy2O3 as the dopant, using a low temperature citrate-auto-ignition method. The samples were sintered at different temperatures retaining the cubic fluorite structure. Rietveld refinement of the X-ray diffraction profiles has given detailed microstructural information of the prepared samples. The transmission electron micrographs confirmed the presence of atomic planes as obtained from X-ray diffraction. The UV-Vis spectra show a red shift of the absorption peak with the increase in sintering temperature. Impedance spectroscopy studies of the samples exhibited thermally activated non-Debye type relaxation process. In addition, studies of the electrical conductivity have suggested the negative temperature coefficient of resistance (NTCR) behavior of the samples. The comparable values of activation energies, obtained from different parameters, indicated that the ions follow the same type of mechanism for conduction as well as for relaxation. The temperature independence of the mechanisms has been confirmed from scaling of different spectra. The correlation between structural and electrical properties of the samples has been discussed and interpreted accordingly.

Microstructure evolution, dielectric relaxation and scaling behavior of Dy-for-Fe substituted Ni-nanoferrites

Dy-substituted nickel nanoferrites have been investigated in order to explore the possibility of Dy-for-Fe substitution in nickel ferrites, as well as the effect of the substitution on the microstructural and electrical properties. The samples were prepared by a simple citrate nitrate auto-ignition method. Rietveld analysis of the X-ray diffraction profiles confirmed the Dy-for-Fe substitution in this spinel ferrite. A slight increase in lattice parameter and microstrain due to incorporation of Dy is observed. The transmission electron microscopy also confirmed the high crystallinity of the prepared samples. It has been found that the doped samples show ionic conductivity 1 to 2 orders greater than that of the undoped sample at a particular temperature. In addition, the doped sample shows lower dielectric loss than the undoped sample. The frequency dependence of the dielectric permittivity has been analyzed using the Havriliak–Negami formalism. The time-temperature superposition principle has been established by the scaling of different spectra.

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.

Optical and ionic transport mechanism γ-phase stabilized nanostructured Bi-Ce-O ionic conductors: a structure-property correlation study

AbstractThis work reports the body-centered cubic (BCC) γ-phase stabilization of Bi2O3 nanostructures by means of varying Ce doping concentration and its effect on the optical, ionic transport and dielectric properties. The Rietveld analysis of X-ray diffraction pattern confirmed the formation of nanocrystalline Ce-doped Bi2O3 composite nanostructure having BCC as main phase in addition with small amount of monoclinic phase at room temperature for 30% doping concentration in the pure Bi2O3 matrix. The results of TEM, EDAX and XRF analysis are consistent with the Rietveld analysis. Lattice fringe and SAED pattern obtained from HRTEM analysis confirm the body-centered cubic γ-phase as dominant phase. The UV-Vis spectroscopy study shows decrease in optical band gap with doping concentration. The presence of different molecular bonds corresponding to γ-phase has been confirmed using FT-IR spectroscopy. The ionic conductivity of the samples has been found to increase with measuring temperature as well as doping concentration. The dielectric and complex modulus properties have been analyzed using Havriliak-Negami formalism and found to be non-Debye type. The conductivity data has been found to obey Variable Range Hopping phenomenon which is corroborated with the structural property of the prepared compositions. Graphical abstractᅟ

Ionic conductivity of rare earth doped phase stabilized Bi2O3: Effect of ionic radius

Nanostructured Bi2O3 was prepared through citrate auto ignition method and stabilized down to room temperature into rhombohedral phase by 30% doping of rare earth cations (Eu3+, Sm3+, Nd3+, La3+), which was experimentally confirmed by the XRD patterns of the doped compositions. The average crystallite size increases with increase of ionic radius. The ionic conductivity of the La-doped compound was found to be highest among other doped compounds. The change in structural and electrical properties were discussed and correlated with the ionic radius of the dopants.

Effect of sintering temperature on structural, optical and electrical relaxation properties of Gd-doped nickel-ferrites

In this work, we report different structural, optical and electrical transport properties of Gd doped Ni-ferrites synthesized through citrate auto ignition method and sintered at different temperatures. The Rietveld refinement of X-ray diffraction patterns confirms the production of Ni-Fe phase with an additional orthorhombic phase GdFeO3. The photoluminescence (PL) spectra shows that PL intensity is higher for higher temperature sintered samples suggesting higher recombination rate of photo generated electron hole pairs. The electrical analysis shows that the conductivity increases with increasing sintering temperatures. The analysis of complex impedance spectra indicates enhanced grain boundary contribution for samples sintered at higher temperatures. Scaling behavior of complex modulus for all the samples at different measuring temperature confirms the validity of time temperature superposition principle (TTSP) and also non Debye type relaxation dynamics in this system. The dielectric loss tangent is f...

Microstructure correlated impedance spectroscopy studies of Ce0.8Y0.2O2-δ: Effect of grain growth

In this work, Y3+ doped ceria particles were prepared though citrate auto ignition method and sintered at different temperatures. The microstructure and electrical properties were found to be affected by the sintering temperature. Impedance spectra confirm the deviation from ideal capacitive nature. The grain and grain boundary conductivity and activation energy were found to depend on the grain growth of samples during sintering. At higher sintering temperature conductivity decreases due to permeate of impurity atoms at grain boundaries and formation of defect clusters. Both the grain and grain boundary capacitance was found to decrease with particle size. The constant phase elements and relaxation time for grain and grain boundaries were found to depend on the sintering temperature. Relaxation time decreases at high sintering temperature due to formation of defect associate.

Charge carrier dynamics in nanocrystalline Dy substituted ceria based oxygen ion conductors

Nano-crystalline Ce1-xDyxO2-δ (x = 0.1-0.5) materials were prepared using the low temperature citrate auto-ignition method. The Rietveld analysis of the XRD data confirmed the single phase cubic fluorite structure. The particle sizes of the sintered samples are in nano range and lattice parameter increases with Dy concentration. Polydispersed and agglomerated particles are observed by SEM. The EDAX spectra show good stoichiometry of the different atoms in the samples. The conductivity is found to have both grain and grain boundary contribution and shows highest value at x= 0.2. The frequency dependence of dielectric permittivity has been analyzed using Havrilliak-Negami formalism. The variation in different electrical properties has been explained by formation defect associates and their interaction with charge carriers.