Metallization in the molten and solid state and phase diagrams of the GeSe$_2$ and GeS$_2$ under high pressure

We found that under high pressure, the GeSe$_2$ and GeS$_2$ melts pass into the metallic state. In the vicinity of the melting curves, their metallization begins at $3.5$ and $7$ GPa, respectively. The position of the semiconductor – metal transition line on the phase diagram for GeSe$_2$ liquid is established. The GeS$_2$-II and GeSe$_2$-III high-pressure crystalline modifications are semiconductors, whereas the GeSe$_2$-III modification at pressures exceeding $3.5$–$4$ GPa is a metal ($\sigma\approx10^3\,\Omega^{-1}\cdot\text{cm}^{-1}$). The $P$, $T$ phase diagrams for these compounds are constructed in the pressure range up to $10$ GPa. Metallization during the GeSe$_2$-II–GeSe$_2$-III transition is evidently responsible for the small jump of entropy and the corresponding almost vertical slope of the transition line.