Pressure-Induced4f−5dElectron Collapse in Ytterbium Monotelluride

The pressure-volume relationship in YbTe has been studied by high-pressure x-ray diffraction up to 300 kbar. This relationship is anomalous in the region 150-190 kbar indicating a continuous electronic collapse with pressure, in which the ${\mathrm{Yb}}^{2+}$ changes to ${\mathrm{Yb}}^{3+}$ state. This must involve $4f-5d$ electron promotion and must result in a semiconductor-to-metal transition. The behavior of YbTe suggests that in rare-earth chalcogenides with large band gap a continuous transition would be favored.