The electrical properties of HgTe and HgSe under very high pressure

The electrical properties of HgTe and HgSe have been investigated at pressures up to 200 kbar in an octahedral apparatus. Measurements of the electrical resistivity at room temperature showed that, beyond the well-known transition from the semimetallic to semiconductive state, both become metallic, at 84 kbar and 155 kbar, respectively. The energy gap at various fixed pressures was obtained from the resistance-temperature relationships. The energy gap of semiconducting HgTe decreases monotonically with pressure, the coefficient being ?l.53 × 10^?5$\text{eV}\text{bar}$. The energy gap of HgSe is rather insensitive to pressures up to 75 kbar, above which it decreases continuously ($\text{dE}\text{dP}$ = ?1.59 × 10^?5$\text{eV}\text{bar}$) before vanishing around 150 kbar. At high pressures the temperature coefficient of the resistance in the metallic state is 3.25 ~ 4.70 × $\text{10}{}^{\mathrm{?3}}\text{deg}$ for HgTe, and 5.7 ~ 5.9 × $\text{10}{}^{\mathrm{?3}}\text{deg}$ for HgSe.