PHASE-TRANSITION PRESSURES OF Fe3O4 AND GaAs DETERMINED FROM SHOCK-COMPRESSION EXPERIMENTS

Abstract Shock-wave technique is used in order to observe the phase transition of two iron oxides, magnetite (Fe3O4) and hematite (αFe2O3), and two semiconductors, GaAs and GaP. Shock data up to about 500 kbar are obtained by streak-camera photography. Phase-transition pressure in magnetite is determined from two inclined mirror runs to be 216 ± 15 kbar, which is appreciably lower than the corresponding value at static pressures, 250 ± 15 kbar. Two inclined mirror runs for GaAs reveal a three-wave structure, yielding a Hugoniot elastic limit and apparent phase-transition pressure of 84 ± 8 kbar and 203 ± 11 kbar. If a correction due to the shear strength effect on the phase transition is taken into consideration, this value is reduced to be 162 ± 11 kbar, which is again remarkably lower than the static value of 193 ± 5 kbar or 180 ± 1 kbar. The observed discrepancy between transition pressures determined from static and dynamic means suggests a partial loss of shear strength in shocked GaAs. Preliminary experiments on αFe2O3 and GaP indicate phase transitions above about 500 kbar and at about 260 kbar respectively.