V. N. Mulay

A STUDY OF ELASTIC BEHAVIOUR AND INTERNAL FRICTION OF ALUMINIUM SUBSTITUTED MAGNESIUM-COPPER FERRITES

Abstract The compressional ( V l ) and shear velocities ( V s ) of polycrystalline Al-substituted MgCu mixed ferrites having seven different compositions have been measured at room temperature by ultrasonic pulse transmission technique. The Youngs modulus ( E 0 ), rigidity modulus ( n 0 ) and bulk modulus ( k 0 ), corrected to zero porosity are found to decrease continuously with increasing Al-content. The variation of elastic moduli with composition has been explained in terms of binding forces between the ions. Internal friction (Q −1 ) for all the specimens has also been determined at room temperature by the pulse-echo technique.

ULTRASONIC ANOMALIES IN Y–Ba–Cu–O HIGH-Tc SUPERCONDUCTING MATERIALS

The longitudinal and shear wave velocities of Y–1–2–3 superconducting materials prepared by the sol–gel method have been measured by the pulse transmission technique over a temperature range of 80–300 K. The longitudinal velocity of both the samples, in general, is found to vary in an anomalous way. The observed behaviour has been explained qualitatively on the basis of a model.

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.

Thermogravimetric analysis of Y1Ba2Cu3O7−δ prepared by different routes

Discussion de 4 methodes chimiques de preparation du compose du titre, des resultats de leur etude par thermogravimetrie, analyse thermique differentielle, diffraction RX et des mesures de resistance electrique a temperature ambiante et de susceptibilite magnetique

Oxidation Behaviour of Infiltrated Reaction Bonded Silicon Carbide

Oxidation studies of reaction bonded silicon carbide (RBSC) infiltrated with vanadium carbide, boron carbide and molybdenum disili- cide (5 wt% each) have been carried out at 1350°, 1400° and 1450°C for 300 minutes. Oxidation resistance of RBSC decreases with addition of the above infiltrants. However, weight gain per unit area is the lowest at higher temperatures (1400°, 1450°C) in case of RBSC infiltrated with vanadium carbide.

Effect of infiltrants on the electrical resistivity of reaction-sintered silicon carbide

The effect of infiltrants on the electrical resistivity of reaction-sintered silicon carbide, at temperatures ranging from RT to 1000°C, has been studied. Electrical resistivity decreases with increase in temperature up to 1000°C in VC and MoSi2, whereas minimum electrical resistivity is observed at ∼600°C in B4C infiltrant.

ELASTIC BEHAVIOR OF Y-1-2-3/SILVER COMPOSITES

A series of Y-1-2-3/Ag high Tc superconducting composites have been prepared using the sol–gel method by sintering at three different sintering temperatures, viz. 910°C, 945°C, and 975°C. After the usual characterization by XRD, electrical resistance, bulk density, and porosity measurements, the longitudinal (V1) and shear wave (Vs) velocities were measured by the pulse transmission technique. Using the experimental data, several elasticity parameters such as Youngs modulus (E), rigidity modulus (G), etc. were evaluated. The variation of elastic constants with dopant concentration has been explained in terms of the binding forces between various atoms of the superconductor. A linear relationship between the superconducting transition temperature (Tc) and the Debye temperature (θD) has also been obtained.

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.