Isothermal compression of magnetite to 320 KB

Abstract

The effect of pressure on the lattice parameter of magnetite has been determined at room temperature up to 320 kbar by means of X ray diffraction employing a diamond anvil high-pressure cell. By using the Birch-Murnaghan equation with a (∂KT/∂P)T∣P=0 value of 4 ± 0.4 the isothermal bulk modulus at zero pressure was calculated to be 1.83 ± 0.10 Mbar. The X ray diffraction study also revealed that at pressures greater than 250 kbar, magnetite transforms to a high-pressure phase, which reverts to magnetite at pressures below 50 kbar. It is possible to index this high-pressure phase as being monoclinic. If it is assumed that the unit cell contains two molecules, the density is in agreement with the density predicted for a phase of Fe3O4 having all of the iron atoms in sixfold coordination.