Transition to a virtually incompressible oxide phase at a shock pressure of 120 GPa (1.2 Mbar): Gd3Ga5O12

Cubic, single-crystal, transparent Gd(3)Ga(5)O(12) has a density of 7.10 g/cm(3), a Hugoniot elastic limit of 30 GPa, and undergoes a continuous phase transition from 65 GPa to a quasi-incompressible (QI) phase at 120 GPa. Only diamond has a larger Hugoniot elastic limit. The QI phase of is more incompressible than diamond from 170 to 260 GPa. Electrical conductivity measurements indicate the QI phase has a band gap of 3.1 eV. Gd(3)Ga(5)O(12) can be used to obtain substantially higher pressures and lower temperatures in metallic fluid hydrogen than was achieved previously by shock reverberation between Al(2)O(3) disks.