Browsing by Author "K.S. Bartwal"

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Current-controlled negative resistance in ZrS2 single crystals
(1992) K.S. Bartwal; O.N. Srivastava
Current-controlled negative resistance (CCNR) in ZrS2 single crystals has been observed at room temperature (about 300K) and liquid N2 temperature (about 77 K). It is shown here that CCNR occurs because of a double injection of carriers coupled with the presence of deep recombination centres in the bulk of the material. © 1992.
Growth and characterization of single crystals in the series ZrSxSe2-x
(1995) K.S. Bartwal; O.N. Srivastava
Single crystals of transition metal dichalcogenide layered compounds with composition ZrSxSe2-x, where x varies within the range 0-2, were grown by the chemical vapour transport technique using iodine as a transporting agent. These binary solid solution crystals are found to be isomorphous over the whole range of composition. The growth conditions and lattice parameters were determined. X-ray diffraction was employed to determine accurate lattice parameters. © 1995.
Metal‐Insulator Transition in Titanium Disulphide Crystals
(1986) B. Das; K.S. Bartwal; O.N. Srivastava
A temperature induced metal (M) → insulator (I) transition is investigated which is possibly first of its kind in the titanium rich titanium disulphide crystals confirming to the composition Ti1.17S2. This transition is established by monitoring the temperature dependence of the electrical conductivity and the thermoelectric power. The structural characteristics at room temperature and at high temperatures (≈ 573 K) also are explored through electron diffraction. The M → I transition is believed tooccur due to the increase of disorder which occurs at high temperature where the short range order state of excess Ti atoms in the van der Waals gapgives rise to a highly disordered amorphous like state. This may lead toshifting of the mobility edge from below the Fermi energy to above the Fermienergy, thus leading to the observed M → I transition. Copyright © 1986 WILEY‐VCH Verlag GmbH & Co. KGaA
Metal‐semiconductor transition in TiS1.7 crystals
(1985) K.S. Bartwal; B. Das; O.N. Srivastava
[No abstract available]
Negative resistance in ZrSe2 single crystals
(1993) K.S. Bartwal; O.N. Srivastava
Voltage-controlled negative resistance (VCNR) has been observed in the semiconducting layered compound ZrSe2 at a field of ∼ 50-100 V cm-1, at room temperature. The occurence of VCNR is attributed to the intervalley transfer of electrons in the conduction band. © 1993.
Order-Disorder phase transformation in ZrS2 single crystals
(1993) K.S. Bartwal; Krishan Lal; O.N. Srivastava
Order-disorder phase transformation has been observed in ZrS2 single crystals on annealing them at a temperature of 400 ± 10°C. Loss of sulphur, resulting in its deficiency, on annealing of crystals is thought to be the cause of the observed phase transformation. Evidence in its support, based on X-ray and electrondiffraction results, is advanced. © 1993, Taylor & Francis Group, LLC. All rights reserved.
Short-and long-range ordering of vacancies in ZrS2 crystals
(1993) K.S. Bartwal; O.N. Srivastava
Electron diffraction has been used to study the structure of ZrS2 single crystals. On annealing these crystals at 400+ 10°C a diffuse intensity distribution has been recorded in the diffraction patterns which has been attributed to short-range ordering of sulphur vacancies. Three different superlattices have been observed to result from the long-range ordering of sulphur vacancies. © 1993 Taylor & Francis Ltd.
Studies of metal-insulator transition in TiSxSe2-x Single Crystals
(1990) K.S. Bartwal; O.N. Srivastava
A temperature induced metal-insulator transition has been found in TiSxSe2-x single crystals. The M-I transition is found to occur over the temperature range 250° to 300°C for 1.0 ≤ x ≤ 1.7. The present observation of the M-1 transition has been compared and contrasted with the earlier reported M-I transition in TiS1, 7 single crystals. Evidence is presented and arguments are put forward in support of the occurrence of the M-I transition in terms of the variation in disorder of the extra Ti atoms in the van der Waals gap. The possible reason for the suppression of the M-I transition in TiSxSe2-x for x ≤ 1 is outlined. © 1990, Taylor & Francis Group, LLC. All rights reserved.
Superlattices in non-stoichiometric ZrS2 single crystals
(1992) K.S. Bartwal; O.N. Srivastava
Electron diffraction has been used to study the structure of ZrS2 single crystals. The as-grown crystals were quenched to liquid nitrogen temperature after annealing at 400°C. Three different (2 × 2) superlattices have been observed resulting from the long-range ordering of sulphur vacancies. © 1992.