Phase transformations in shock-compressed ytterbium

In order to study the phase transformations of ytterbium under shock compression, the electrical resistance of ytterbium at the initial temperatures of $77$ and $290$ K and a shock pressure of $p\le20$ GPa is measured. The dependence of ytterbium resistance on pressure is nonmonotonic and indicates three successive phase transitions. At $p\approx2$ GPa, ytterbium enters a state with a high electrical resistance of the semiconductor type. The ytterbium bandgap at $p\approx1.8$ GPa is estimated as $\approx0.02$ eV. At $p\approx3$ GPa, the electrical resistance of ytterbium decreases due to a polymorphic phase transition The electrical resistance grows with further increase in pressure, and at $p>11$ GPa, it does not change. The nature of the third transition is determined by calculating the temperature of the sample under shock compression. Analysis of the dependence of sample temperature on shock pressure, together with the phase diagram of ytterbium, suggests that the third transition is caused by ytterbium melting.