D. Suresh Babu

Dielectric studies of Fe Doped SmCrO3 Perovskites

Polycrystalline Fe doped SmCrO3 perovskite ceramics were prepared by sol-gel route and characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), dielectric and Impedance measurements. Single-phase perovskite Fe doped SmCrO3 obtained has been confirmed from the XRD pattern with orthorhombic structure. The dielectric properties of perovskite Fe doped SmCrO3 ceramics were studied in the frequency range of 100Hz – 1MHz in the temperature range from 80 K to 300 K. These materials exhibited colossal dielectric constant value of ~ 104 at room temperature. The response is similar to that observed for relaxor-ferroelectrics. To get the detailed information, IS data analysis was performed.

MAGNETIC RELAXATION, LOWER CRITICAL FIELD AND IRREVERSIBILITY LINE OF W DOPED (Bi, Pb)-2223 SUPERCONDUCTOR

We report magnetic relaxation, lower critical field and irreversibility line studies of a single phase W doped (Bi,Pb)-2223 superconductor. The temperature dependence of remanent magnetization exhibited a rapid drop at T ≤ 20 K and was due to the drastic decrease of critical current density (Jc). The activation energy U0 determined from magnetic relaxation measurements showed that there exists two types of pinning centres in the vortex lattice. The temperature dependence of lower critical field (Hc1) exhibited a kink around 25 K. Possible reasons for exhibited anomaly in Hc1 were discussed. The irreversibility line exhibited an exponential decrease with increasing temperature and is due to the existence of break down field of proximity effect, induced superconductivity in layered HTSC. Fermi velocity in superconductivity regions (VFN) is found to be a factor of ten larger than that in normal regions (VFN).

NON-RESONANT MICROWAVE ABSORPTION STUDIES ON BI-V-SR-CA-CU-O SUPERCONDUCTING SYSTEM

Microwave absorption studies have been carried out on samples Bi2Sr2Ca2Cu3Oy (sample A) and Bi1.6V0.4Sr2Ca2Cu3Oy (sample B). dc microwave absorption studies of these samples showed that sample A had a small volume of 2223 phase and a large volume of 2212 phase, whereas sample B had a single 2223 phase. Variation of LFMA signal amplitude of sample A with temperature showed definite peaks at 97 K and 70 K which may correspond to the 2223 and 2212 phases. In the case of sample B it showed a single peak at 90 K corresponding to the 2223 phase. The average Josephson loop diameter was estimated for these samples and found to be 1.23 μm to 3.11 μm and 0.7 μm to 1.86 μm for samples A and B respectively.

Preparation and characterization of perovskite Cu doped LaFeO3 semiconductor ceramics

Orthorhombic structured polycrystalline Cu doped LaFeO3 perovskite ceramics were prepared by sol-gel route and characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopic (FT-IR) techniques. The complex dielectric properties for these ceramic samples investigated as function of temperature, in the range 80K – 300K, and frequency, in the range 20 Hz -1MHz. These samples exhibiting colossal dielectric constant value of 104 near room temperature at low frequencies. The response is similar to that observed for relaxor ferroelectrics. Impedance spectroscopy (IS) data analysis indicates the ceramics to be electrically heterogeneous semiconductors consisting of semiconducting grains with dielectric constant below 100. We conclude, therefore that grain boundary effects is the primary source for the high effective dielectric constant in Cu doped LaFeO3 ceramics.

STUDY OF PINNING BEHAVIOR OF VORTEX LATTICE IN Bi1.6Pb0.3W0.1Sr2Ca2Cu3Oy SUPERCONDUCTING SYSTEM

We report characterization and detailed magnetization study in fields up to 2 T in the temperature range between 5 and 80 K of Bi1.6Pb0.3W0.1Sr2Ca2Cu3Oy (nominal composition pellets). XRD, field-cooled magnetization measurements, and electrical resistance studies showed that the sample consists of a single phase high-Tc (Bi-2223) superconductor in addition to CaWOy-type impurity. An empirical magnetic phase diagram of the superconducting system has been derived. We determined a H*(T) line where Jc becomes zero. In the region with nonzero critical current density, vortex lattice exhibits mainly two types of pinning behaviours, single vortex and collective pinning behaviour, in different field and temperature range. In addition, the temperature dependence of Jc showed an evidence of two types of pinning centres. In low temperatures (<40 K), the pinning centers with low values of activation energy are active whereas in high temperatures (≥40 K), the pinning centers with larger activation energy are active. T...

Vanadium doped Bi2Sr2Ca2Cu3Oy superconducting ceramics

Abstract We report here the preparation of the B2−xVxSr2Ca2Cu3Oy ceramic superconductors with x ranging from 0 to 1. These samples were characterized by using X-ray diffraction, DC electrical resistivity and AC susceptibility measurements. From the results of X-ray diffraction and DC electrical resistivity we have found that two phases appear in these samples. One is identified as the 2212 phase (low Tc phase) and the other is identified as the 2223 phase (high Tc phase). The critical temperature of the 2223 phase is observed to be higher than that of the pure bismuth case subject to a similar preparation process. The above measurements showed that the high Tc phase (2223) increases with an increasing concentration of vanadium at the expense of the low Tc phase (2212).

Magnetic properties of PrCr 1−x Fe x O 3 Perovskite

PrCr1-xFexO3(PCFO) samples were prepared by citric acid route. The samples were characterized by XRD and SEM. The sample exhibits a single phase orthorhombic structure with Pbnm space group. The Temperature dependent and field dependent magnetic measurements are measured in the range of 5K-400K at 100 Oe field and isothermal magnetization curves were recorded in the field range +5T to -5T at 5K temperature. The substitution of Fe3+ in Cr3+ site increases the Cr-O-Fe ferromagnetic superexchange interaction and thus increase in magnetic moments, with maximum at x=0.8. The frustration of co-existence of antiferromagnetism and ferromagnetism leads to decrease of magnetic ordering transition temperature from 240K (x=0) to 98K (x=0.8).

Synthesis and dielectric properties of Fe doped SmCrO3semiconductor ceramics

Polycrystalline Fe doped SmCrO 3 perovskite ceramics were characterized by X-ray diffraction (XRD). The dielectric properties of perovskite Fe doped SmCrO 3 ceramics were investigated in the frequency range of 100Hz - 1MHz in the temperature range from 80 K to 300 K. These materials exhibited colossal dielectric constant value of ∼ 104 at room temperature. The response is similar to that observed for relaxorferroelectrics. To get the detailed information IS data analysis was performed.

Synthesis and dielectric properties of Fe doped SmCrO[sub 3] semiconductor ceramics

Polycrystalline Fe doped SmCrO 3 perovskite ceramics were characterized by X-ray diffraction (XRD). The dielectric properties of perovskite Fe doped SmCrO 3 ceramics were investigated in the frequency range of 100Hz - 1MHz in the temperature range from 80 K to 300 K. These materials exhibited colossal dielectric constant value of ∼ 104 at room temperature. The response is similar to that observed for relaxorferroelectrics. To get the detailed information IS data analysis was performed.

Giant dielectric constant in Cu doped LaFeO3

Orthorhombic structured polycrystalline Cu doped LaFeO3 perovskite ceramics were prepared by citric acid route and characterized by X-ray diffraction (XRD), The complex dielectric properties for these ceramic samples investigated as function of temperature, in the range 80K - 300K, and frequency, in the range 20 Hz-1MHz. These samples exhibiting colossal dielectric constant value of 104 near room temperature at low frequencies. The response is similar to that observed for relaxor ferroelectrics. To clarify this speculation, the Impedance data analysis performed.