• Volume 3, Issue 4

December 1981,   pages  389-454

• Dislocation network patterns in tungstenite single crystals

TEM studies of tungstenite crystals grown by sublimation method have been investigated. Different types of dislocation network patterns were observed. The observed network patterns in bright field are compared with weak beam dark field pictures and the results are discussed.

• Thermopower of$$Ag_{2 + \delta }$$S across theα-β transitionacross theα-β transition

Thermopower data of$$Ag_{2 + \delta }$$S in both of itsα- andβ-phases are reported and the results are compared with the data on$$Ag_{2 + \delta }$$Se.

• New chemical methods for the deposition of Cu1·8S and TlSe thin film

New chemical methods for the deposition of thin film of Cu1·8S and TlSe have been developed. The deposition of Cu1·8S thin film has been performed by thiourea, ammonia and Cu2+ ions at room temperature, while TlSe thin films are obtained from triethanolamine as complexing agent, ammonia, sodium selenosulphate solution and Tl1+ ions at room temperature. The electrical resistance, mobility, carrier concentration and optical band gap have been measured.

• Van der Waals coefficients and cohesive energies of lead chalcogenides

The cohesive energies of PbS PbSe and PbTe, having NaCl type of crystal structure, are calculated using the generalized Huggins-Mayer form (GHM) for the Born repulsion energy. The van der Waals interactions (VDW) are estimated from the London and Mayer formulae and compared with those estimated from the Slater-Kirkwood variational method. The cohesive energies calculated adopting the VDW coefficients calculated from the later method are in good agreement with the experimental values. The difference between the experimental cohesive energies and the calculated, assuming variational method, are 2·26, 2·97 and 3·75 eV respectively for PbS, PbSe and PbTe which are in good agreement with the reported values for the covalent bonding correction using Heitler-London-Lowdin method (HLL) which are respectively 2·1, 2·9 and 3·3 eV (Tanaka and Morita 1979).

• Galvanomagnetic properties of plastically deformed InSb single crystals

The dc Hall effect, dc conductivity and mobility have been studied on deformed and undeformed samples ofn-type InSb from liquid nitrogen temperature to room temperature. These studies have shown that the Hall coefficient values of deformed samples do not differ much from undeformed sample, but a considerable amount of change was observed in mobility, suggesting that equal number of donor and acceptor type dislocations are introduced during the deformation process. In addition the mobility variation of the deformed samples with temperature has shown a peak in 170–300°K range. The dislocation mobility (μD) is deduced from the observed mobilities of deformed and undeformed samples. The plotμD vs T has two regions, region 1 being independent of temperature and region 2 having a linear increase with temperature. Theβ factor obtained from region 2 is found to be almost equal to the one calculated from Dexter and Seitz model. The dislocation densities at room temperature are also calculated for the deformed samples using the above model.

• Dielectric and polarization studies on some organic materials

Dielectric constant and dielectric loss (tanδ) of oxamide, thiooxamide, urea, thiourea and some methyl and ethyl derivatives of urea and thiourea have been measured. The deformation polarization for all the materials is calculated from the static dielectric constants. The electronic contribution to molecular polarization has been evaluated theoretically using atomic hybridization components. The atomic polarization is obtained as the difference between the deformation polarization and electronic contribution to the deformation polarization.

• Etch pit shapes on {110} surfaces of CaF2 crystals

{110} surfaces of CaF2 crystals are etched with different concentrations of HCl. It is found that concentrated HCl produces characteristic rectangular pyramidal etch pits and 2 volume percent HCl produces boat shaped etch pits. Such variations in the etch pit shapes on {110} surfaces of CaF2 crystals with different concentrations of HCl have been explained. Concentrated H2SO4 is found to be a suitable chemical polisher for these surfaces, the polishing rate is about 0·1μ/min.

• On the sintering kinetics of titania doped ceramic lanthanum chromite

The sintering behaviour of lanthanum chromite with the addition of 1 to 3 wt% TiO2 was studied. Densification was examined as a function of sintering temperature and TiO2 concentration. The results showed that pure LaCrO3 could not be densified to &gt;75% of the theoretical density, while the densities exceeding 90% of the theoretical were achieved with 3 wt% titania addition at 1600° C.

Metallographic study reveals a normal grain growth following the rate equationD2D02=kt. Activation energies both for densification and grain growth have been estimated to be ≈ (80±5) k cal/mole in case of 3 wt% TiO2 addition.

• Determination of the composition of binary systems by the ratio method employing SEM-EDAX

By employing x-ray emission in a scanning electron microscope (SEM), it has been shown that compositions of binary systems such as As-Se glasses, Al-Zn alloys and copper sulphides can be determined.

• SEM-studies of tin-iodide whiskers

Optical and scanning electron microscopic observations have been made of tin-iodide whiskers crystals grown by the gel-method. Most of the whiskers have been found to be of two types: (i) hollow and (ii) solid whiskers. The observations indicate that the formation of hollow whiskers is possible with or without the presence of impurities. By using electron micro probe, the overgrowth of tin-tetra iodide crystals on tin-iodide whisker crystals have been identified. A growth mechanism for tin-iodide whiskers have been suggested. The implications are discussed.

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