H. N. K. Sarma

Electrical and magnetic studies of the spinel system Li0.5+tCrxSbtFe2.5-x-2tO4

The lattice constant, dc resistivity, dielectric constant, saturation magnetization and Curie temperature were studied on a series of Cr-substituted Li-Sb ferrite systems. The dc resistivity increases with increase of the chromium level. A change in slope was observed in the variation of resistivity with temperature and hence two regions of different activation energy. The study of dielectric permittivity with frequency showed dispersion for the whole system. The saturation magnetization and the Curie temperature were found to decrease with increase of the substitution level.

Influence of Co2+ on the electrical and magnetic properties of Li–Sb ferrites

Abstract Investigations have been carried out on the electrical properties of polycrystalline Li–Sb ferrites, when successively substituted with Co2+ ions. The samples with compositions Li0.6−0.5xCoxSb0.1Fe2.3−0.5xO4, (0.0≤x≤1.0 in steps of 0.2) were prepared by the double sintering ceramic technique. XRD method confirmed all the samples to be single-phase spinels. The decrease in resistivity is reported as a function of composition and temperature. The decrease in resistivity with composition has been attributed to the cation distribution and the presence of cobalt ions in the two valence states at the octahedral site. All the samples exhibit a change in slope in the plot of resistivity vs. inverse temperature, giving two regions with a large variation in activation energy. A dispersion with frequency was observed in the dielectric behaviour of all the samples, studied in the frequency range of 100 Hz to 1 MHz. Peaks were observed in the tan δ vs. frequency curve for all the samples x=0.4 and 0.8. The possible mechanisms involved are discussed. The observed decrease in the Curie temperature with cobalt content and the compositional dependence of room temperature saturation magnetization are explained on the basis of Neels model and the cation distribution.

OPTICAL AND STRUCTURAL PROPERTIES OF NANO-SIZED BARIUM STRONTIUM TITANATE (Ba0.6Sr0.4TiO3) THIN FILM

Barium strontium titanate (Ba0.6Sr0.4TiO3) or BST thin films on quartz substrates have been prepared by using a modified sol-gel processing technique. The starting materials are barium 2-ethylhexanoate Ba[CH3(CH2)3CH(C2H5)CO2]2, strontium 2-ethylhexanoate Sr[CH3(CH2)3CH(C2H5)CO2]2 and titanium (IV) isopropoxide Ti[CH3CH3CHO]4. The precursors Ti[CH3CH3CHO]4 except were synthesized in the laboratory. Transparent and crack-free films were fabricated on quartz substrates by spin coating. The as-fired films were found to be amorphous, which crystallized to cubic phase after annealing at 550°C in air for 1 hr. In this paper, we report the structural and optical properties of BST thin films prepared by the modified sol-gel process.

DIELECTRIC PROPERTIES OF Li-Sb FERRITES

Dielectric properties such as dielectric constant (e′) and dielectric loss tangent (tan δ) of Li0.5+xFe2.5-2xSbxO4 ferrites, 0.10≤ x ≤0.30 in steps of 0.05 have been investigated as a function of composition, frequency and temperature. The dielectric constant showed dispersion with frequency in the range of 100 Hz–1 MHz. Peaks were observed in the tan δ versus frequency curves for almost all the samples. The temperature variation of dielectric constant for the different samples was studied at 10 kHz in the temperature range from room temperature to 433 K. Peaks were observed for some of the samples. The peaks were seen to shift towards higher temperature region as the substitution level increases. The mechanisms involved in the processes are discussed in this paper.

Dielectric Properties of Vanadium Substituted Lithium Zinc Titanium Ferrites

This paper reports the influence of vanadium substitution on the properties of Li–Zn–Ti ferrite. Samples with compositional formula Li0.5+tZn0.2Ti0.2VtFe2.1-2tO4 (t ranging from 0 to 0.25 in steps of 0.05) were prepared by the conventional sintering technique. XRD analysis confirmed all the samples to be single phase with spinel structure. The lattice constant a density, Curie temperature and Saturation magnetization were measured. The dielectric behaviour was studied as a function of frequency and temperature. The dielectric behaviour showed dispersion with the frequency in the range 100 Hz to 1 MHz. The dielectric constant increases with the increase of temperature for all the samples. The possible mechanisms involved are discussed.

ELECTRICAL CONDUCTION IN SUBSTITUTED Li-FERRITES PREPARED BY MICROWAVE PROCESSING

Samples with representative formula Li0.45Ni0.1Mn0.1Fe2.35O4 have been sintered by conventional sintering technique and microwave sintering technique. Both the samples showed single-phase with spinel structure. The lattice constant for the microwave sintered (MS) sample showed a lower value than the conventionally sintered (CS) sample. The density of the MS sample has been found to be higher than the CS sample. And MS sample showed a higher value of resistivity and activation energy compared to the CS sample. The possible mechanisms are discussed.

MÖSSBAUER EFFECT STUDIES ON LITHIUM FERRITE SUBSTITUTED WITH CHROMIUM AND ANTIMONY

The effect of Cr3+ concentration on the various hyperfine interactions for the ferrite system Li0.5+tCrxSbtFe2.5-2t-xO4, 0.0 ≤ x ≤ 1.0, x in steps of 0.2 and t = 0.1, have been studied at room temperature using Mossbauer spectroscopy. The isomershift and the quadrupole splitting are almost negligibly influenced by the change in chromium level. The internal nuclear magnetic field, as determined from the Mossbauer spectra and the linewidth are also studied with the variation of composition. The results have been explained on the basis of various models and a cation distribution has been worked out.

Structural and Optical Properties of Barium Strontium Titanate (Ba0.5Sr0.5TiO3) Thin Films

Ferroelectric Barium Strontium Titanate (Ba0.5Sr0.5TiO3) or BST thin films on quartz substrates have been prepared by using a modified sol gel processing technique. The starting materials are Barium 2-ethylhexanoate Ba[CH3(CH2)3CH(C2H5)CO2]2, Strontium 2-ethylhexanoate Sr[CH3(CH2)3CH(C2H5)CO2]2 and Titanium(IV) isopropoxide [TiOCH(CH3)2]4. The precursors except [TiOCH(CH3)2]4 were synthesized in the laboratory. Transparent and crack-free films were fabricated on quartz substrates by spin coating. The as-fired films were found to be amorphous, which crystallized to cubic phase after annealing at 550°C in air for 1 hr. In this paper we report the structural and optical properties of BST films prepared by the modified sol-gel process. Communicated by Prof. E. C. Subbarao

DIELECTRIC PROPERTIES OF Ni2+ AND Mn3+ SUBSTITUTED Li-FERRITE PREPARED BY MICROWAVE SINTERING TECHNIQUE

Li0.45Ni0.1Mn0.1Fe2.35O4 ferrite samples were prepared by microwave-sintering (MS) and conventional (CS) techniques. XRD studies have confirmed the single-phase spinel structure of the sample. The lattice constant was found to be 8.334 A which is lower than that of the conventionally sintered (CS) sample. Upon microwave sintering, improved physical and electrical properties (like density, resistivity etc.) were obtained. A comparative study has been made on the dielectric behavior of samples processed by both techniques. The possible mechanisms are discussed.

HYPERFINE INTERACTION STUDIES OF Co2+ SUBSTITUTED Li-Sb FERRITE SYSTEM

Mossbauer investigations have been carried out for the system Li0.6-0.5xCoxSb0.1-Fe2.3-0.5xO4 with 0.0≤x≤1.0, x in steps of 0.2. The observed variation of the various Mossbauer parameters like isomershift, quadrupole splitting, nuclear magnetic field and linewidth are explained in terms of cation distribution and superexchange interaction.