Electrical conductivity measurements of stannic iodide

Abstract

Conductivity measurements on insulating molecular materials can be of practical use, but are subject to considerable uncertainty because of variations in carrier density caused by extrinsic factors such as internal purity and perfection, ambient gases and photogeneration of carriers. During the past decade, single crystals of stannic iodide (SnI4) have been the subject of optical and electrical investigations. These studies have advanced the quantitative understanding of photodissociation [ 1 ], photolysis [2] and luminescence [3] of SnI4 materials. The optical absorption edge measures the gap between the conduction and valence bands, in the absence of excitation states and strong impurity absorptions. Whall and Juzova [4] have used the techniques Of transient photoconductivity to investigate the carrier transport in SnI4. Applied research has recently put forward SnI4 as a humidity proof transparent antistatic film coating [5]. SnI4 is an attractive molecular solid having a simple tetrahedral molecule which condenses into crystals of a simple cubic structure and with perfect octahedral habit. The tin and iodine atoms are covalenfly bonded while the intermolecular forces are entirely of van der Waals' type. As far as the authors are aware, electrical conductivity measurements of SnI4 have not been reported in the literature. In this paper, we have reported the behaviour of electrical conduction in the temperature range 30 to l l 0 ° C to understand the mechanism of electrical conduction in SnI4. Single crystals of SnI4 (Fig. i) used in the present investigation were grown by employing the gel-technique [6]. Orange to reddish octahedral SnI4 crystals up to 5 mm in size were obtained. The grown crystals were examined by scanning electron microprobe analysis, X-ray diffraction, density measurements and thermogravimetric analysis, these techniques confirmed that they were SnI4. By chemical analysis the percentage of tin and iodine in SnI4 were estimated as 15% and 83%, respectively. For pellet samples, the laboratory grown crystals were finely ground and the resulting powders, of average particle size 150/am, were compressed in a die under a pressure of 200 kg cm -2, giving a packing fraction of 0.764. The crystal or the pellet, as the case may be, was mounted between the flat platinum electrodes in an ordinary conductivity cell. It was then enclosed in a resistance heated furnace, and the temperature of the sample was monitored using