The cation distribution in magnesioferrite MgFe2O4 was investigated using a “piston-cylinder” apparatus at three pressures (ambient, 1, and 2 GPa) over a temperature range of 600 to 1200 °C. Quenched samples of magnesioferrite were investigated by X-ray powder diffraction. The inversion parameter was derived from the unit-cell parameter at ambient temperature.
The inversion parameter increases with pressure, being a smooth function of P-T conditions. The changes in the cation distribution in magnesioferrite caused by the changes in P-T conditions produce the contributions to the bulk modulus (<0.01%) and thermal expansion coefficient (12–60%). On average, the pressure increment of 0.01 GPa is compensated for by 1 °C heating.
The effect of pressure on the cation ordering obeys the fundamental relationship (dV/dx)T,P (dx/dP)T < 0. The terms are (dV/dx) < 0 and (dx/dP) > 0 for MgFe2O4 and MgAl2O4.