B. K. Das

Effect of doping a Mn-Zn ferrite with GeO 2 and SnO 2

The effects of various additions of GeO 2 or SnO 2 , in a Mn-Zn ferrite on the microstructure and magnetic properties have been studied. The behavior of GeO 2 additive has been found to be similar to that of SiO 2 . Up to a GeO 2 content of 0.64 mol%, the magnetic properties improve through the increase in the density. At a higher GeO 2 content of 1.28 mol%, the properties deteriorate due to the occurrence of discontinuous grain growth. Further addition of GeO 2 gives better grain structure but poor properties. The presented results suggest that Ge4+dissolves in the ferrite to a very limited extent and GeO 2 exists as a second phase. SnO 2 , on the other hand, has been found to be soluble in the ferrite and does not alter the microstructure even up to a content of 5.70 mol%. The essential property of this additive is found to be in its ability to modify the variation of μ i with temperature without deteriorating the μ i and core losses. The temperature variation of the bulk resistivity has also been studied.

Screen printed titanium oxide and PECVD silicon nitride as antireflection coating on silicon solar cells

Silicon nitride and titanium oxide coatings have been used to reduce the reflection losses from silicon solar cells. Both 100-mm-diameter circular and 100 × 100 mm pseudo-square single crystalline silicon solar cells have been used in the present studies. More than 27% enhancement in the short circuit current has been demonstrated in polished cells using screen printed titanium oxide antireflection coating. Solar cells made from textured silicon wafers were used for plasma enhanced CVD grown silicon nitride antireflection coating on them. In these cells more than 23% enhancement in short-circuit current has been observed after silicon nitride antireflection coating.

Influence of V 2 O 5 addition on electrical conductivity and magnetic properties of Ni-Zn ferrites

The effect of V 2 O 5 addition on the electrical and magnetic properties of iron-deficient Ni-Zn ferrites has been studied. A maximum in the initial permeability, a minimum in the dc electrical conductivity, and the loss factor were observed at a V 2 O 5 content of 0.4 mol%, irrespective of the sintering temperature. The results obtained can be explained in terms of solubility of V 2 O 5 in the ferrite matrix.

On the origin of core losses in a manganese zinc ferrite with appreciable silica content

The effect of silica on the magnetic properties and microstructure of a manganese zinc ferrite has been studied. It is found that as silica content increases, the magnetic properties at first improve, then deteriorate around 0.04% silica due to discontinuous grain growth. At still higher silica contents, magnetic properties deteriorate further due to an increase in the total effective magnetic anisotropy.

Determination of minority‐carrier diffusion length in a p‐silicon wafer by photocurrent generation method

A nondestructive method to determine the diffusion length of minority carriers in a p‐silicon wafer is outlined. This novel method is based on creating an accumulation layer on one side and an inversion layer on the other side of the wafer by depositing thin semitransparent layers of high (e.g., palladium) and low (e.g., aluminum) workfunction metals, respectively. The wafer acquires a structure akin to p+‐p‐n+ and is capable of generating a photocurrent when illuminated. The photocurrent Isc (where sc represents short circuit) as a function of the intensity Pin of a monochromatic radiation incident on the accumulation layer (p+) side of the wafer is measured. The diffusion length L is determined from the slope of the Jsc vs Pin curve. The values of L so determined were compared with that determined from the measurement of spectral response by illuminating the wafer from the inversion layer (n+) side and were found to be in excellent agreement.

Oxidation studies of Y-Ba-Cu superconducting oxides

Abstract The oxidation characteristics of quenched samples of Y-Ba-Cu-O system, using thermogravimetric analysis (TGA); differential thermal analysis (DTA) and X-ray diffraction analysis, has been reported. A weight gain of 3.75% has been recorded in thermogravimetry experiment. The observed 3.75% change in weight of the quenched sample during heating or cooling cycle may be attributed to the multiphase compound formation due to decomposition reaction in the sample at 950°C.

The influence of second phase precipitation on SiO 2 /GeO 2 doped Ni-Zn Ferrite properties

SiO 2 and GeO 2 have been found to have limited solubility in the Ni-Zn ferrite. SiO 2 having negligible solubility is seen to segregate as a dispersed phase, which reduces grain boundary mobility during sintering. Unreacted GeO 2 (m.p. ≃ 1100°C), on the other hand, forms a free flowing liquid phase, which wets the grain and promotes faster grain growth during sintering. The initial permeability decreases significantly with increasing GeO 2 additions. The bulk conductivity σ dc of the samples containing higher concentrations of these dopants shows an anamolous temperature dependence which is typical to the Schottky thermoionic emission. Such phenomena are discussed in terms of the second phase precipitation. The domain wall energy γ is also seen to increase significantly at higher dopant concentrations reflecting an increase in the internal stresses, caused primarily by these precipitates.

Non-superconducting phase stability in YBa2Cu3O7−x compound

Abstract The non-superconducting phases in 123 superconducting compound YBa2Cu3O7-x using X-ray diffraction pattern have been studied. The 123 superconducting phase has been found to decompose on isothermal heating at 750°C. The growth of non-superconducting phases has been accelerated in the presence of traces of CO2 gas which is normally present in air and oxygen gas of commercial grade. These phases are quite stable once they have formed.

Growth kinetics of thin anodic oxides of silicon and its dependence on phosphorus concentration in silicon

Abstract A model has been proposed to study the growth kinetics of thin (no more than 300 A thick) oxides of silicon, anodically grown at constant voltage by using ethylene glycol +0.04 N NH4NO3 as the electrolyte. The thickness of oxide is found to vary linearly with applied voltage at a rate of 6 A V−1 for a phosphorus concentration in silicon of 1 × 1015 atoms cm−3 which decreases to 5.5 A V-1 and 5 A V−1 for a phosphorus concentration of 8 × 1020 atoms cm−3 and 1.3 × 1021 atoms cm−3 respectively. The dependence of the rate of oxidation and other rate constants on phosphorus concentration in silicon have also been studied.

Transport current and microstructure in Y1Ba2Cu3O7−x superconductors

Abstract Bulk polycrystalline Y1Ba2Cu3O7−x samples have been synthesized by ceramic, chemical and melting techniques. Transport critical current density (Jct) of the samples of ceramic and chemical methods has been measured and found very low compared to the Jc values calculated from the magnetization measurements and theoretical depairing critical current density. Here Jct values are interpreted in terms of the microstructure. The poor Jct is attributed to weak links such as, besides grain boundaries, twin boundaries, microinhomogeneity regions within and on the grain and twin boundaries, intrinsic structural disorder and inter and transgranular microcracks which may be responsible for superconducting glassy state and lath or plate type anisotropic grains distributed randomly. The work described here further reveals that fine needle shaped grain morphology is realised by melting technique and higher Jct values could be obtained of the long axes needle type grains are aligned along the length of superconducting rod or wire.