Glassy selenium at high pressure: Le Chatelier's principle still works

Selenium is the only easily vitrified elementary substance. Numerous experimental studies of glassy Se ($g$-Se) at high pressures show a large spread in the data on the compressibility and electrical resistivity of $g$-Se. Furthermore, H. Liu et al. [Proc. Natl. Acad. Sci. USA 105, 13229 (2008)] have arrived at the surprising conclusion that the volume of glass increases during pressure-induced crystallization. We have performed high-precision measurements of the specific volume and electrical resistivity of glassy selenium ($g$-Se) at high hydrostatic pressures up to 9 GPa. The measured bulk modulus at normal pressure is $B=(9.05\ifmmode\pm\else\textpm\fi{}0.15)$ GPa and its pressure derivative is ${B}_P^{\ensuremath{'}}=6.4\ifmmode\pm\else\textpm\fi{}0.2$. In the pressure range $\mathrm{P}<3$ GPa, glassy selenium has an anomalously large negative second derivative of the bulk modulus. The electrical resistivity of $g$-Se decreases almost exponentially with increasing pressure and reaches 20 $\mathrm{\ensuremath{\Omega}}$ cm at a pressure of 8.75 GPa. The inelastic behavior and weak relaxation of the volume for $g$-Se begin at pressures above 3.5 GPa; the volume and logarithm of the electrical resistivity relax significantly (logarithmically with the time) at pressures above 8 GPa. Bulk measurements certainly indicate that the volume of $g$-Se glass in the crystallization pressure range is larger than the volumes of both appearing crystalline phases (by 2% and 4%). Therefore, the ``volume expansion phenomenon'' suggested in [H. Liu et al., Proc. Natl. Acad. Sci. USA 105, 13229 (2008)] is not observed, and the pressure-induced crystallization of glassy selenium is consistent with the laws of thermodynamics.