Viscosity and Electrical Conductivity Measurements and Results

The viscosities of Te, HgTe, Hg0.9Cd0.1Te, Hg0.8Cd0.2Te, and Hg0.84Zn0.16Te melts were measured. Earlier in the research, the viscosities of HgTe, Hg0.8Cd0.2Te and Hg0.84Zn0.16Te melts have been measured by an oscillating-cup (OC) viscometer. However, the long duration for the measurements by OC, approximately an hour of continuous data collection, prevented the studies of systems with shorter relaxation time. Therefore, a novel transient torque viscometer (TTV) was developed to rapidly measure the viscosity by creating a rotating flow of the melt in the presence of a uniform rotating magnetic field (RMF). The measured transient rotation of the ampoule can be used to determine the viscosity of the melt. Because this transient process finishes in very short time, the required measurements can be completed within two minutes. More importantly, with the Lorentz force introduced by the RMF to the melt, the electrical conductivity can also be simultaneously measured as the torque that induced by the interaction between the RMF and the melt is a linear function of electrical conductivity of the melt. Then the viscosity of Te, HgTe, Hg0.9Cd0.1Te and Hg0.8Cd0.2Te melts and the electrical conductivity of the solids and melts of Te, HgTe, Hg0.9Cd0.1Te and Hg0.8Cd0.2Te were measured by TTV. The measured viscosity by TTV showed more consistency and less scattering comparing to the data obtained from the OC method. The theoretical analyses on the viscosity data of Te melt indicate a structural transition occurring in the liquid around 873 K, about 150 K above its melting point, which is consistent with the finding on the density of the liquid Te given in Chap. 4. The analyses of the measured viscosity on the melts of HgTe, Hg0.9Cd0.1Te and Hg0.8Cd0.2Te implies a structural transition approximately at 1078 K and 1066 K, respectively, for HgTe and Hg0.9Cd0.1Te and no structural transition in the measured temperature range for the Hg0.8Cd0.2Te melt. The measured electrical conductivity of the solids indicated a characteristic of metals or degenerate semiconductors. Above the melting point of HgTe and the solidus temperatures of Hg0.9Cd0.1Te and Hg0.8Cd0.2Te, the measured electrical conductivity increases with increasing temperature, indicating a semiconductor-like behavior. As the temperature increasing, the measured electrical conductivity started to reach saturated values, implying a metallic behavior. The time relaxation behavior was studied by monitoring viscosity and electrical conductivity after rapidly lowering the sample temperature after long time soaking at elevated temperature. Two samples out of these melts, Hg0.84Zn0.16Te and Hg0.8Cd0.2Te, showed relaxation behavior although their trends were different. During the relaxation, the viscosity of the Hg0.84Zn0.16Te melt continuously increased by about 50% to reach its steady state value after 120 h whereas the viscosity for the Hg0.8Cd0.2Te melt went through a maximum and then decreased 62% to its equilibrium value in about 60 h. At the same time, the measured electrical conductivity of Hg0.8Cd0.2Te melts initially decreased and reached a minimum at approximately 3.4 h then it increased 5% to the equilibrium value after 50 h.