The electrical properties of molybdenite, particularly the measurements of conductivity, Hall effect and thermo-electric power

• Main Author: Salam, Mohamed Salah El-Din Abdel
• Published: Royal Holloway, University of London 1953
• Subjects: 549; Physical Chemistry
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.703707

A study is made of the electrical properties of natural crystals of molybdenite. The conductivity and Hall coefficient for 25 specimens were measured at room temperature. It was found that the majority of the specimens were p-type semiconductors. Measurements of the conductivity and Hall coefficient have been carried out on 6 specimens, selected with widely varying impurity content, over the temperature range from 90°K to 800°K. It is deduced from these measurements that MoS2 is an impurity semiconductor up to 870°K. At higher temperatures, conduction may be ionic. The most important result deduced from the conductivity and Hall effect measurements, is that the nature of the mobility of charge carriers has been established. For the first time, it is verified experimentally that the scattering of the charge carriers in a semiconducting binary compound is mainly due to thermal vibrations of the lattice except at low temperatures when impurity scattering becomes important. There have been numerous theoretical papers concerning the process of the scattering of charge carriers in semiconductors, but the experimental verification of these theories has been almost negligible, except in the case of elements ( Ge and Si ).Room temperature measurements of the transverse change of the conductivity in a magnetic field have been carried out on nine specimens when the field was perpendicular to the basal plane of the crystal. Agreement between the results and theory isobtained, confirming that the scattering of charge carriers is a lattice effect. The value of the mobility calculated from these measurements are in reasonable agreement with that obtained from the conductivity and Hall effect measurements. The change in conductivity when a magnetic field is applied parallel to the basal plane of the crystal, has been investigated and the results suggest that the motion of the charge carriers are confined to the basal plane. The variation with temperature of the concentration of charge carriers, derived from the Hall constant, is discussed. The Hall coefficient is constant at room temperaturefor magnetic fields up to 28,000 oersteds. The thermoelectric power has been measured for 4 specimens in the temperature range from 90°K to 700°K. Good agreement is obtained between the results and theory above room temperature.the Ettingshausen, Nernst and Righi-Leduc effects, have been investigated and the results compared with theory.