Displacive transition in magnesiowustite

Magnesiowustite (Mg0.1Fe0.9)O was studied at ambient temperature under both hydrostatic and quasihydrostatic pressures to 35 GPa. The elastic behaviour, equation of state, transition pressure, and the structure before and after the B1-rhombohedral transition were determined. K-0- and K'(0)-values for the B1 phase were calculated to be 155 +/- 10 and 3.6 +/- 0.8 GPa respectively under hydrostatic conditions. The second-order B1-rhombohedral transition occurred at 20 GPa. Quasihydrostatic conditions were used to determine the stress/strain in different crystallographic directions to elucidate the transition mechanism which is triggered by the softening of the c(44) in the B1 phase. (Some figures in this article are in colour only in the electronic version).