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High-pressure/high-temperature experiments have been carried out to investigate the possibility of pressure-induced metallization in thallium iodide (TlI). Earlier studies predicted pressure-induced metallization on the basis of a decrease in the activation energy of electrical conduction with increase in pressure. High temperature electrical resistance measurements in the multianvil apparatus, using 10/5 assemblies, document the change in conductivity behavior characterizing a transition from the semi-conducting to metallic state. The temperature dependence of resistance is negative for semi-conductors but positive for metals. The distinctly different behavior shown at pressures bracketing the transition in the figures below suggest the possibility of exploiting TlI and similar materials in smart devices for use in applications where band-gap related electrical properties can be tuned by the environmental pressure conditions.

Fig. 3.2-16: Temperature dependence of electrical resistance of TlI at various pressures showing a transition from semi-conducting to metallic behavior. The signature decrease in resistance with increasing T and P for the semi-conducting phase is shown for data at 8.7 and 9.5 GPa. At 10.0 GPa however, the T dependence of resistance reverses sign and becomes positive but the pressure dependence of resistance remains negative which heralds the onset of metallization.