S G Patel
Articles written in Bulletin of Materials Science
Volume 24 Issue 3 June 2001 pp 291-296 Optical Properties of Materials
The optical energy gaps of WS2 single crystal were determined from the analysis of the absorption spectrum near the fundamental absorption edge at room temperature using light parallel to 𝑐-axis incident normally on the basal plane. On the basis of two- and three-dimensional models it was found that both direct and indirect band transitions took place in WS2 and the indirect transition was of the allowed type. The optical energy gaps corresponding to both transitions were determined and the phonon energies associated with the indirect transitions estimated. The implications of the results have been discussed.
Volume 26 Issue 6 October 2003 pp 569-574 Semiconductors
Single crystals of ternary mixed compounds of group IV–VI in the form of a series, SnS𝑥Se1-𝑥 (where 𝑥 = 0, 0.25, 0.50, 0.75 and 1), have been grown using direct vapour transport technique. The grown crystals were characterized by the X-ray diffraction analysis for their structural parameter determination. All the grown crystals were found to be orthorhombic. The microstructure analysis of the grown crystals reveals their layered type growth mechanism. From the Hall effect measurements Hall mobility, Hall coefficient and carrier concentration were calculated with all crystals showing 𝑝-type nature. The d.c. electrical resistivity measurements perpendicular to 𝑐-axis (i.e. along the basal plane) in the temperature range 303–453 K were carried out for grown crystals using four-probe method. The d.c. electrical resistivity measurements parallel to 𝑐-axis (i.e. perpendicular to basal plane) in the temperature range 303–453 K were carried out for the same crystals. The electrical resistivity measurements showed an anisotropic behaviour of electrical resistivity for the grown crystals. The anisotropic behaviour and the effect of change in stoichiometric proportion of S and Se content on the electrical properties of single crystals of the series, SnS𝑥Se1-𝑥 (where 𝑥 = 0, 0.25, 0.50, 0.75 and 1), is presented systematically.
Volume 27 Issue 1 February 2004 pp 23-25 Single Crystals
NbTe2 is a member of transition metal dichalcogenide (TMDC) group. Single crystals of niobium ditelluride (NbTe2) have been grown by a chemical vapour transport technique using iodine as transporting agent. The composition of the grown crystals was confirmed on the basis of energy dispersive analysis by X-ray (EDAX) and remaining structural characterization was also accomplished by X-ray diffraction (XRD) studies. Lattice parameters, volume and X-ray density have been carried out for the grown crystals. The particle size for a number of reflections has been calculated using Scherrer’s formula.
Volume 27 Issue 2 April 2004 pp 213-216 High Pressure Studies
Single crystals of MoS2 and MoSe2 were grown by chemical vapour transport method using iodine as a transporting agent and characterized by optical microscopy, energy dispersive analysis (EDAX), X-ray powder diffraction (XRD) and Hall mobility at room temperature. The variation of electrical resistance under pressure was monitored in a Bridgman anvil set-up up to 6.5 GPa to identify occurrence of any structural transition. MoS2 and MoSe2 do not undergo any structural transitions under pressure.
Volume 28 Issue 5 August 2005 pp 405-410 Single Crystals
Single crystals of the lamellar compound, ZrSe3, were grown by chemical vapour transport technique using iodine as a transporting agent. The grown crystals were characterized with the help of energy dispersive analysis by X-ray (EDAX), which gave confirmation about the stoichiometry. The optical band gap measurement of as grown crystals was carried out with the help of optical absorption spectra in the range 700–1450 nm. The indirect as well as direct band gap of ZrSe3 were found to be 1.1 eV and 1.47 eV, respectively. The resistivity of the as grown crystals was measured using van der Pauw method. The Hall parameters of the grown crystals were determined at room temperature from Hall effect measurements. Electrical resistivity measurements were performed on this crystal in the temperature range 303–423 K. The crystals were found to exhibit semiconducting nature in this range. The activation energy and anisotropy measurements were carried out for this crystal. Pressure dependence of electrical resistance was studied using Bridgman opposed anvils set up up to 8 GPa. The semiconducting nature of ZrSe3 single crystal was inferred from the graph of resistance vs pressure. The results obtained are discussed in detail.
Volume 31 Issue 4 August 2008 pp 645-654 Single Crystals
A series of zirconium sulphoselenide (ZrS𝑥Se3–𝑥, where 𝑥 = 0, 0.5, 1, 1.5, 2, 2.5, 3) single crystals have been grown by chemical vapour transport technique using iodine as a transporting agent. The optimum condition for the growth of these crystals is given. The stoichiometry of the grown crystals were confirmed on the basis of energy dispersive analysis by X-ray (EDAX) and the structural characterization was accomplished by X-ray diffraction (XRD) studies. The crystals are found to possess monoclinic structure. The lattice parameters, volume, particle size and X-ray density have been carried out for these crystals. The effect of sulphur proportion on the lattice parameter, unit cell volume and X-ray density in the series of ZrS𝑥Se3–𝑥 single crystals have been studied and found to decrease in all these parameters with rise in sulphur proportion. The grown crystals were examined under optical zoom microscope for their surface topography study. Hall effect measurements were carried out on grown crystals at room temperature. The negative value of Hall coefficient implies that these crystals are 𝑛-type in nature. The conductivity is found to decrease with increase of sulphur content in the ZrS𝑥Se3–𝑥 series. The electrical resistivity parallel to c-axis as well as perpendicular to 𝑐-axis have been carried out in the temperature range 303–423 K. The results obtained are discussed in detail.
Volume 43, 2020
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