Semiconducting Region of Ytterbium

The resistivity of elemental ytterbium at room temperature rises, by a factor of 11, to a maximum at a pressure of 40 kilobars; a further increase in pressure causes a polymorphic transition; the new phase has a resistivity 80 percent of that of the metal at 1 atmosphere. In the temperature-pressure diagram, the phase boundary has a negative slope. The phase boundary, determined from -190 degrees to 360 degrees C, is a straight line that may be extrapolated nearly to the known alpha-beta transition at 1 atmosphere. Between the transition pressure and 20 kbar, the lowest pressure at which the measurements were made, ytterbium behaved as a semiconductor. The temperature coefficient of resistance is negative; at constant pressure, the resistivity shows the exponential temperature dependence characteristic of a semiconductor. The parameter in the expontial would correspond to an energy gap 0.015 ev at 20 kbar, an increase with pressure to a maximum of 0.080 ev at 37 kbar, and then a decrease to 0.05 ev at 45 kbar.