J. Sobhanadri

Bio: J. Sobhanadri is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Dielectric & Intercalation (chemistry). The author has an hindex of 10, co-authored 42 publications receiving 725 citations. Previous affiliations of J. Sobhanadri include Madurai Kamaraj University.

DC conductivity and dielectric behaviour of cobalt-zinc ferrites

Abstract: DC conductivity and dielectric studies of CoxZn1−xFe2O4 (x = 0.32, 0.49, 0.79), BaFe12O19, and Mg0.25Zn0.75Fe2O4 are reported as a function of temperature and frequency. The lattice constant and the existence of a single phase are established from X-ray studies. The dielectric behaviour is attributed to the Maxwell-Wagner polarisation. A dispersion region is observed in one of the cobalt-zinc ferrites and the barium ferrite. Activation energies are calculated for these two ferrites from dielectric measurements. The conductivity of these ferrites is explained by the hopping mechanism. Activation energies and the transition temperatures are presented. Ergebnisse von Gleichstromleitfahigkeits- und dielektrischen Untersuchungen an CoxZn1−xFe2O4 (x = 0,32; 0,49; 0,79) BaFe12O19 und Mg0,25Zn0,75Fe2O4 in Abhangigkeit von der Temperatur und Frequenz werden mitgeteilt. Die Gitterkonstante und die Existenz einer einzelnen Phase werden aus den Rontgenuntersuchungen festgestellt. Das dielektrische Verhalten wird der Maxwell-Wagner-Polarisation zugeschrieben. Ein Dispersionsbereich in einem der Kobalt-Zink-Ferrite und der Barium-Ferrite wird beobachtet. Fur diese beiden Ferrite werden aus den dielektrischen Messungen Aktivierungsenergien berechnet. Die Leitfahigkeit dieser Ferrite wird durch einen Hopping-Mechanismus erklart. Aktivierungsenergien und Ubergangstemperatur werden angegeben.

The far-infrared spectra of some mixed cobalt zinc and magnesium zinc ferrites

Abstract: The far-infrared spectra of five mixed ferrites in the range 200 to 640 cm−1 are reported. Four bands are observed. The high frequency band (v1) and low frequency band (v2) are assigned to the tetrahedral and octahedral complexes, respectively. A small band (v3) around v2 is observed and its intensity increases with divalent octahedral metal ion concentration. This band is assigned to the octahedral divalent metal-oxygen ion complexes. The lowest band observed for the highest concentration of cobalt is attributed to the lattice vibrations of the system. Die Ferninfrarot-Spektren von funf Mischferriten im Bereich 200 bis 640 cm−1 werden mitgeteilt. Vier Banden werden beobachtet. Die hochfrequente Bande (v1) und die niederfrequente Bande (v2) werden den'tetraedrischen bzw. oktaedrischen Komplexen zugeordnet. Eine schwache Bande (v2) bei v2 wird beobachtet, deren Intensitat mit der Konzentration divalenter oktaedrischer Metallionen zunimmt. Diese Bande wird den oktaedrischen divalenten Metall-Sauerstoff-Komplexen zugeordnet. Die niedrigste Bande, die fur die hochste Kobaltkonzentration beobachtet wird, wird den Gitterschwingungen des Systems zugeschrieben.

Electrical conductivity of some nickel‐zinc ferrites

Abstract: The electrical conductivity of some nickel-zinc ferrites is studied as a function of temperature. The ferrites with iron in excess show n-type conduction and those with iron in deficiency show p-type conduction. Seebeck coefficient, X-ray analysis, and saturation magnetisation are also carried out to discuss the conductivity of these ferrites. Es wird die elektrische Leitfahigkeit einiger Nickel-Zinkferrite als Funktion der Temperatur gemessen. Ferrite mit Eisenuberschus zeigen n-Leitfahigkeit, solche mit Eisenmangel p-Leitfahigkeit. Untersuchungen des Seebeckkoeffizienten, der Sattigungsmagnetisierung sowie Rontgenanlysis werden durchgefuhrt, um die Leitfahigkeit dieser Ferrite zu diskutieren.

Electrical conductivity and thermoelectric power measurements of some lithium–titanium ferrites

Abstract: The electrical conductivity and thermoelectric power of some lithium–titanium ferrites with small amounts of manganese and zinc have been studied as a function of temperature in the range of 300–550 K and are reported here. The conductivity variation shows two different regions with a large variation in the activation energies. The possible mechanisms with respect to ionic conduction and electron hopping are discussed with the support of thermoelectric power measurements. Lattice parameters are also calculated from x‐ray diffractograms for confirming the single‐phase nature of the ferrites.

The measurement of the properties of materials

Abstract: This review covers approximately 15 years of development in the techniques used to measure dielectric properties of materials over the frequency range 1 MHz to 1500 GHz. An introductory section summarizes the broad development trends and is followed by short sections which deal with developments at a more detailed level. The approaches described include time- and frequency-domain methods; reflection, transmission, and resonant methods, guided and free-space methods; discrete-frequency and broad-band methods, especially Fourier Transform Spectroscopy. Measurements on magnetic materials are also briefly discussed.

Electrical conductivity and dielectric behaviour of nanocrystalline NiFe2O4 spinel

Abstract: Electrical conductivity and dielectric measurements have been performed for nanocrystalline NiFe2O4 spinel for four different average grain sizes, ranging from 8 to 97 nm. The activation energy for the grain and grain boundary conduction and its variation with grain size have been reported in this paper. The conduction mechanism is found to be due to the hopping of both electrons and holes. The high-temperature conductivity shows a change of slope at about 500 K for grain sizes of 8 and 12 nm and this is attributed to the hole hopping in tetrahedral sites of NiFe2O4. Since the activation energy for the dielectric relaxation is found to be almost equal to that of the dc conductivity, the mechanism of electrical conduction must be the same as that of the dielectric polarization. The real part e' of the dielectric constant and the dielectric loss tanδ for the 8 and 12 nm grain size samples are about two orders of magnitude smaller than those of the bulk NiFe2O4. The anomalous frequency dependence of e' has been explained on the basis of hopping of both electrons and holes. The electrical modulus analysis shows the non-Debye nature of the nanocrystalline nickel ferrite.