N. Srinivasan

High resolution electron density mapping for LiF and NaF by maximum entropy method (MEM)

Abstract High resolution maximum entropy method (MEM) electron density maps have been elucidated for LiF and NaF using reported X-ray structure factors. The ionic nature of the bonding between constituent atoms in both the systems is found to be well pronounced and clearly seen from the electron density maps. The resolution of the present MEM maps is 0.063xa0A per pixel for LiF and 0.072xa0A per pixel for NaF along the three crystallographic axes. The electron density at the middle of the bond along [111] is found to be 0.0673xa0e/A3 for LiF and 0.003xa0e/A3 for NaF showing the different ionic strengths of the bonding. The electron density along [100] and [110] has also been drawn and analyzed. The inequality in the ionicity for the individual atoms and the electron content for different ionic radii have also been analyzed and compared with already published results. The wRMEM obtained from MEM analysis is 0.3% for LiF and 0.79% for NaF.

An investigation on the bonding in MgO, CaO, SrO and BaO from the MEM electron density distributions

The bonding in MgO, CaO, SrO and BaO has been studied using the electron density distribution maps obtained utilizing the reported X-ray data by the statistical approach maximum entropy method (MEM). The ionic/covalent nature of the bonding and the interaction between the atoms are clearly revealed by the maps. The bonding in these systems is shown two-dimensionally on the (100) and (110) planes and the one-dimensional electron density profiles along (100), (110) and (111) directions have also been plotted using MEM electron densities. The electron density at the saddle point between the ions has been estimated using these profiles and compared with the available reported results. The resolution of these maps is high and hence these maps can be regarded as the most precise electron density distributions seen inside the chosen materials. The electron content of the doubly ionic oxygen and the cations are estimated from the three-dimensional MEM electron densities by assuming spheres of various radii. The histograms drawn with [FMem(k)−FObs(k)]/σ(k) versus the number of reflections show the validity of the approach and the appropriateness of the Gaussian weighting scheme used in the analysis.

Synthesis and characterization of some ferrite nanoparticles prepared by co-precipitation method

Two different compositions of ferrites namely Ni0.53Cu0.12Zn0.35Fe2O4 and Mg0.2Cu0.3Zn0.5Fe2O4 have been synthesized by co-precipitation method and sintered at 900xa0°C/5h. The prepared samples are analyzed for their structural, morphology, elemental composition and magnetic properties by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence and vibrating sample magnetometer respectively. Spinel phase, along with the hematite as an additional phase, in both samples is confirmed from the XRD characterizations results. Rietveld refinement method is employed to analyze the structural parameters of the samples. Density and saturation magnetization have found to be increased from that of undoped sample values. Homogeneous distributions of particles and well defined particle sizes are revealed from SEM studies of the samples. Maximum entropy method is employed to compute the numerical value of various sites interactions in ferrites and the findings are compared and analyzed with that of magnetic studies.

Effect of sintering on dielectric and AC conductivity properties of Ni0.5Zn0.5Fe2O4 nano ferrite particles

The dielectric properties such as dielectric constant both real and imaginary part, dielectric loss factor, and AC resistivity have been studied in this work on mechanically alloyed Ni0.5Zn0.5Fe2O4 nano ferrite particles sintered from 700 to 1200xa0°C as a function of frequency in the range of 0.1xa0Hz to 15xa0MHz. The dielectric constant (ε′) decreases with increase in sintering temperature and the decrease is explained with proper mechanism. The samples sintered at 900 and 1200xa0°C show slightly high ε′ value compared to their predecessor. The AC resistivity at room temperature is found to be of the order of 109xa0Ω-cm.