No abstract

No abstract

The behaviour of iron in ZnS has been studied through the effect of iron concentration on magnetic and electrical properties. Specimens containing iron in amounts varying from 0.09 to 16.16 atom per cent have been synthesized. These were found to be homogeneous by electron-probe microanalysis and under the reflecting microscope. At lower iron concentrations the synthetic and natural iron-bearing sphalerites are paramagnetic and their magnetic susceptibilities vary with the iron content in a linear manner. At higher iron concentrations these iron-bearing sphalerites become increasingly antiferromagnetic and their magnetic susceptibilities vary in a non-linear manner. The antiferromagnetic behaviour may be comparable to that observed in Mn-bearing ZnS and is probably the result of similar magnetic ordering of the substitutional iron. Electrical conduction for a natural iron-bearing sphalerite has been found to result from migration of low-mobility holes rather than by electrons. This observation is consistent with the mechanism known as d-band conduction, which attributes electrical current to the flow of holes in the d-bands of transition metals. This type of conduction is possible in iron-containing ZnS through the interaction of Fe+ with Fe2+, with the Fe3+ in either the tetrahedral or the octahedral position.

The movement of silver, gold, and copper in single-crystal bismuth telluride has been measured, parallel t o the cleavage planes, as a function of temperature for two current densities. At the lower current density (150 A/cm2) movement occurred always to the cathode. At the higher current density (250 A/cm2) a transition occurred from cathodic movement below about 300 "C t o bipolar movement-to both the anode and the cathode. This effect remained in evidence up t o about 400 "C with an increasing tendency t o anodic migration with increase of temperature. By about 400 OC essentially all transport occurred to the anode.The bipolar movement is considered t o be due t o the metal ions occupying two types of sites in the bismuth telluride lattice where different electrical forces are present.Similar experiments with iodine-doped bismuth telluride indicated negligible movement of iodine under co~nparable conditions.

No abstract