In-Situ Conductivity Measurement of BaF₂ under High Pressure and High Temperature

We perform the in-situ conductivity measurement on BaF₂ at high pressure using a microcircuit fabricated on a diamond anvil cell. The results show that BaF₂ initially exhibits the electrical property of an insulator at pressure below 25GPa, it transforms to a wide energy gap semiconductor at pressure from 25 to 30GPa, and the conductivity increases gradually with increasing pressure from 30GPa. However, the metallization predicted by theoretical calculation at 30--33GPa cannot be observed. In addition, we measure the temperature dependence of the conductivity at several pressures and obtain the relationship between the energy gap and pressure. Based on the experimental data, it is predicted that BaF₂ would transform to a metal at about 87GPa and ambient temperature. The conductivity of BaF₂ reaches the order of 10^-3\Omega^-1cm^-1 at 37GPa and 2400K, the superionic conduction is not observed during the experiments, indicating the application of pressure elevates greatly the transition temperature of the superionic conduction.