The results of microstructural investigations on bulk YBa₂Cu₃O₇ prepared by melt growth process are reported.

In this paper a radioactive tracer technique based on sliding cell method developed in our laboratory for the study of diffusion in liquids is presented in detail. This method consists of radioactive and non-radioactive liquid columns of equal length and the radiation detector is placed in a vertical geometry over the diffusion column. Some liquid metals and aqueous electrolyte solutions were studied by this method. The data of liquid metals like mercury and gallium have been analyzed from the point of view of hard sphere model and those of electrolyte solutions from phenomenological theories. Onsager’s coefficientsL₁₁,L₁₂,L₂₂ have been calculated from the experimental data and the variation of diffusion with solute concentration has been explained from ion-ion interaction.

A nonlinear lattice dynamical theory is proposed to explain the mode softening in intermediate valence compound Sm_0.75 Y_0.25 S. In this theory we consider the breathing motion of the electron shells of Sm-ion to be nonlinear, and depend on temperature, resulting in strong electron-ion coupling. We calculate the salient features of the nonlinear breathing potential, which resembles theφ⁴ potential for second order ferro-electric transitions. We also calculate the temperature dependence of LO(L) frequency for this compound, showing that at transition temperature (about 200 K) this mode freezes.

The contact conduction electron density in metallic dysprosium has been calculated following the APW formalism and taking into account the effects of correlation and spin-polarization. A comparison of this density with that obtained from the Mössbauer isomer shift measurement has been made. An estimate of Δ〈r²〉, the change in mean square nuclear charge radius between the two levels involved in theγ transition, has been made and compared with those obtained by other workers.

The observed O 1s X-ray photoemission spectra of the cuprate superconductors often exhibit a satellite at a higher binding energy to the main peak. The origin of this satellite is not fully understood. We have done model cluster calculations to investigate the origin of this satellite using the configuration interaction approach. The calculated spectra for the divalent and superconducting cuprates essentially exhibit a single peak. On distorting the cluster in-plane, the peak shifts to higher binding energies. This substantiates a deterioration of the surface leading to the observed satellite structure in the O 1s core-level photoemission spectra of the cuprate superconductors.

Electrical resistivity measurements under pressure and lattice parameter study on SmSe_1−xAs_x are reported here. The estimate d lattice parameter and valence is calculated for the same and they are found to be in good agreement with the experimental data. The electrical conductivity increases with the increase of As concentration.

Electrical switching has been observed ino-tolidine-DDQ at pressures of 7.66 GPa and fields ∼3×10⁵V/m withσ_ON/σ_OFF≈10³ at a temperature of 300 K. The switching is found to be of the memory type and the sample can be driven back to the low conducting state by applying ac pulses of sufficient magnitude but independent of frequency.

An experimental method is described to determine the excitation energy migration coefficient Λ in an organic liquid scintillator by measuring the energy transfer rate parameterk₃ and the quenching rate parameterk_7b as a function of temperature in the range of 20°C–70°C. In this experiment we have used toluene as donor, ethyl-1-n-butyl-2-methyl-5-hydroxyindole-3-carboxylate (EBMHC) as acceptor and bromobenzene as quencher. The values of Λ are found to be in good agreement with literature values. Hence this method can be used to determine the migration coefficient in organic liquid scintillators.

Studies of breakdown threshold intensity for air at various pressures in the range of 24–760 torr using 0.355, 0.532 and 1.06 µm radiation are reported. We observep^−0.8 scaling ofI_th at 1.06 µm and a weak scaling ofp^−0.4 at 0.532 and 0.355 µm radiation. Strong dependence of breakdown spot size on laser power but weak dependence on air pressure is observed.