Pressure-induced metallization of MnO

Optical absorption and IR reflection measurements of MnO were performed under various pressures up to 140 GPa at room temperature. In IR reflection measurement, a drastic increase in reflectivity due to the metallization is observed from 94 GPa. On the other hand, in absorption, it is observed that the band gap does not close monotonously with pressure but accelerated extremely from 80 GPa, as indicated by an abrupt increase of an additional absorption tail located at the lower energy than the absorption edge. The absorption tail extends to 0 eV around 90 GPa, which is consistent with the IR reflection measurement. The pressure coefficient of the band gap shift is obtained to be -0.016 eV/GPa up to 80 GPa.