V. Devender Reddy

Far-infrared spectral studies of some lithium-nickel mixed ferrites

Abstract The far-infrared spectra of Li-Ni mixed ferrites reveal four absorption bands (two at high frequencies and two at low frequencies) in the frequency range 700-200 cm -1 . The high-frequency band ( v 1 ) is assigned to the tetrahedral metal complexes, while the absorption bands v 2 and v 3 are attributed to the octahedral metal complexes. On the other hand, the lowest-frequency band ( v 4 ) is attributed to the lattice vibrations of tetrahedral metal ions. It has been observed that all the principal bands of both the unsubstituted and 0.06 mol of nickel-substituted lithium ferrite samples are found to exhibit a shoulder; the phenomenon is explained as being due to the splitting of the main bands, which itself is attributed to the presence of Fe 2+ ion content on octahedral sites.

Electrical transport properties of manganese-magnesium mixed ferrites

Abstract Thermoelectric power studies are made of MnMg mixed ferrites over the temperature range 300–700 K by the differential method. The Seebeck coefficient S is found to decrease while the carrier concentration n and the charge carrier mobility μ are found to increase with increasing temperature. On the basis of these results an explanation for the conduction mechanism in MnMg mixed ferrites is suggested.

Charge transport in mixed LiTi ferrites

Abstract Thermopower studies on mixed LiTi ferrites have been undertaken over the temperature range 300–900 K by the differential method. On the basis of the sign of the Seebeck coefficient Q , the ferrites under study have been classified as n-type semiconductors. Data on the temperature variation of the Seebeck coefficient data have been used to obtain the variation in charge carrier concentration n and mobility μ with temperature for all the samples.

THE INFLUENCE OF SPIN-REORIENTATION ON THE DIELECTRIC BEHAVIOUR OF COBALT SUBSTITUTED W-TYPE BARIUM–ZINC HEXAGONAL FERRITES

Dielectric measurements of cobalt substituted W-type barium–zinc hexagonal ferrites are undertaken both as a function of frequency and temperature. The dielectric constant is found to decrease continuously with increasing frequency while it increases continuously with increasing temperature. The variation of dielectric constant with dopants concentration is explained on the basis of magnetic cation orientation. From the temperature variation of dielectric constant two transitions, one due to the spin reorientation in the temperature range 450–500 K and the other one due to a ferri to paramagnetic transition have been observed. Suitable explanations for the observed behavior are given.

Far-infrared spectra of lithium-titanium mixed ferrites

Abstract The far-infrared spectra of Li 0.5+0.5 a Fe 2.5−1.5 a Ti a O 4 reveal two prominent bands v 1 and v 2 and two weak bands v 3 and v 4 in the 700−200 cm −1 range. The high frequency bands v 1 and v 2 are assigned to tetrahedral metal complexes. On the basis of the analysis of the IR bands and their correlation with the cation distribution, the band v 3 is assigned to octahedral divalent metal ion-oxygen complexes, while the lowest frequency band v 4 is attributed to the lattice vibrations in the mixed ferrites. The splitting of the IR spectral band is explained on the basis of Fe 2+ ion concentration.

ELECTRICAL CONDUCTIVITY OF COBALT-SUBSTITUTED BaZn-W HEXAGONAL FERRITES

The D.C. electrical conductivity of cobalt substituted BaZn-W hexagonal ferrites has been studied as a function of composition and temperature over a temperature range of 300–800 K. It has been observed that the cobalt doping has no influence on the RT values of electrical conductivity, although it does affect many other physical properties. For the first time, the authors noticed two clear and distinct transitions in the conductivity vs. temperature plots of all the samples, the first being ≈475 K and the second near their Curie temperatures. The transition T1 has been attributed to the spin reorientation while the second could be due to the Curie temperature. The activation energy values obtained for the paramagnetic region are found to be higher than those of the ferrimagnetic one for all the samples.

CATION DISTRIBUTION OF LITHIUM–TITANIUM MIXED FERRITES

Cation distribution of Li–Ti mixed ferrites was derived from Seebeck coefficient measurements. The distribution of titanium on octahedron sites is found to increase continuously while the concentration of Fe3+ and Fe2+ are found to decrease rapidly. The data is very much useful to interpret the electrical properties of these materials.

CHARGE TRANSPORT AND CONDUCTION MECHANISM OF COPPER SUBSTITUTED MAGNESIUM ALUMINIUM FERRITES

Electrical conductivity (σ) and thermopower (S) studies of polycrystalline copper substituted magnesium aluminium ferrites of different composition were investigated in the temperature range 300–800 K. Plots of log (σT) versus 103/T are almost linear and show a clear transition near the Curie temperature. On the basis of the sign of Seebeck coefficient, all the samples under investigation have been classified as n-type semiconductors. The temperature variation of Seebeck coefficient curves also exhibited a well defined magnetic transition at the Curie temperature. Using the temperature variation of charge carrier mobility a conduction mechanism in these ferrites is suggested.