Volume 12, Issue 2
July 1989, pages 95-169
pp 95-99 July 1989
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.
pp 101-106 July 1989
The d.c. electrical conductivity of sodium vanadate, rubidium vanadate, cesium vanadate and their solid solutions sodium-rubidium vanadate and sodium-cesium vanadate were studied by a two-probe method in the temperature range covering their transition points. The electrical conductivity shows sharp change at the phase transition temperature of these materials. In NaVO3, RbVO3 and CsVO3, increase in d.c. conductivity is observed in the ferroelectric region while nonlinearities are observed above transition temperatures. In solid solutions, the activation energy in the paraelectric state is higher than that in the ferroelectric state and depends upon sodium concentration.
pp 107-115 July 1989
Results of measurement of d.c. electrical conductivity σ from 85 to 550 K are reported for eleven glass compositions of the Cd-Ge-As system. Three regions are seen in theσ-T data of all these glasses. In region I (85 to 140 K),σ is essentially constant and independent of temperature. In region II (200 to 430 K),σ is thermally activated with a single activation energy. In region III (>430 K) a sudden increase is seen inσ with temperature. From an analysis of the results, it has been possible to identify the mechanism of hopping conductivity among localised ‘defect’ states with region I, normal band type conductivity due to carriers excited to the extended states with region II and thermally assisted memory switching with region III.
In the composition dependence ofσ and ΔE for the CdGexAs2 glasses, special features are seen at the composition Cd28·57 Ge14·28 As57·15, which has equal mol fractions of CdAs2 and CdGeAs2. For the Cd2Ge-As glasses also, a maximum in ΔE and a minimum inσ are seen at this composition.
pp 117-121 July 1989
Glasses in the Li2O:B2O3:Ag2SO4 system were prepared with varying silver sulphate contents. From the present results it can be said that the amorphous matrix accepts Ag2SO4 up to 5 mol% without any devitrification. The enhancement in conductivity with change in the structure of metaborate glass is due to Ag2SO4.
pp 123-127 July 1989
The dielectric response of phlogopite mica has been measured for frequency lying between 10 mHz and 10 kHz with humidity as a parameter. The measured complex capacitance shows a low frequency dispersion (LFD) at high humidities. A weak loss peak is also present at high frequencies and low humidity levels.
pp 129-132 July 1989
Dielectric hysteresis properties of undoped and dysprosium-doped potassium vanadate have been studied in the temperature range covering their transition points. The coercive field of these materials was measured by the hysteresis loop method. It is observed that the coercive field of KVO3 doped with Dy2O3 at different concentrations (0 to 3 mol%) is remarkably dependent on doping concentration. It is also seen that undoped KVO3 shows ferroelectric behaviour up to 320°C while Dy2O3-doped KVO3 samples show ferroelectric behaviour up to 380°C for all concentrations.
pp 133-136 July 1989
The dielectric hysteresis property of sodium vanadate, rubidium vanadate, cesium vanadate and their solid solutions has been studied in the temperature range covering their transition points. The hysteresis loop method is used for coercive field measurements. It was observed that the coercive field decreases with increasing temperature, and that it also decreases with increasing sodium concentration in the solid solutions (sodium-rubidium) vanadate and (sodium-cesium) vanadate.
pp 137-141 July 1989
The effect of alkali and alkaline earth oxides on the crystallization of lithia-alumina-silica glasses has been studied. Crystallization behaviour of glasses has been investigated using DTA and XRD techniques. The principal crystallization phases are identified asβ-spodumene solid solution and lithium metasilicate. The crystallization temperature of glasses decreases with increase in the values of the ionic field strength of the alkali and alkaline earth cations. Addition of these oxides at lower concentrations has no significant effect on the crystalline phases.
pp 143-146 July 1989
Single crystals of triammonium citrate are grown from aqueous solution and characterized using X-ray and etching studies. Using single crystal X-ray diffraction, the crystal is found to be orthorhombic with lattice parametersa = 6·223 Å,b = 15·048 Å andc = 11·056 Å. Surface studies on the as-grown faces reveal stratigraphic patterns. Of the several etchants tried, glacial acetic acid appears to be the best etchant for revealing dislocation sites on the as-grown faces.
pp 147-152 July 1989
A new solid state test cell having a configuration of (−) Ag, Ag6I4WO4/Ag6I4WO4/I2, ABTS (+) [ABTS: 2,2′-azinobis (3-ethylbenzothiazole-6-sulphonate)] has been investigated through polarization and ageing studies. The cell has an open circuit voltage and short circuit current of 640 mV and 18·5µA respectively at room temperature.
pp 153-157 July 1989
Electrically conductive processible polyaniline films have been synthesised from the electropolymerization of aniline under non-aqueous conditions. The characterization of the polymer was carried out by spectroscopic methods.
pp 159-162 July 1989
Thin films of Al-2 wt% Li alloy are prepared on well-cleaned glass substrates by vacuum evaporation at room temperature. Electrical conductivity studies of both alloy Al(Li) and pure Al films show that they obey the logarithmic rate law during the initial period of oxidation. The addition of lithium, however, increases the oxidation rate considerably during the initial period of oxidation. Surface analysis by laser Raman spectroscopy indicates the existence of LiO2 and Al2O3 as the most probable oxide components.
pp 163-169 July 1989
Recent reports on highly efficient photoelectrochemical solar cells withn-type WSe2 have prompted us to grown-type single crystals of WSe2 using a chemical vapour transport method. Different transporting agents have been used. It is seen that SeCl4 transporter leads to very large single crystals ofp-type WSe2, whereas the same transporting agent with excess amount of Se leads ton-type single crystals. PEC solar cells fabricated withp-type andn-type crystals thus grown have been reported and the results discussed.
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