Effects of high pressure and high temperature on cation ordering in magnesioferrite, MgFe (sub 2) O (sub 4) , using in situ synchrotron X-ray powder diffraction up to 1430 K and 6 GPa

Disorder in stoichiometric magnesioferrite, MgFe (sub 2) O (sub 4) , was determined from in situ synchrotron powder X-ray diffraction data [lambda = 0.3738(4) Aa] at 6, 5, and 3 GPa and temperatures up to 1430 K. The a unit-cell parameter increases linearly on heating at the three different pressures. Higher pressures cause a smaller cell volume, as expected. Cation order was analyzed in terms of the inversion parameter, x, { (super iv) [Mg (sub 1-x) Fe (sub x) ] (super vi) [Mg (sub x/2) Fe (sub 1-x/2) ] (sub 2) O (sub 4) } and the order parameter Q = 1-(3/2)x. As pressure increases, the inversion parameter increases in inverse MgFe (sub 2) O (sub 4) spinel. O'Neill and Navrotsky (1983) and Landau models were used to describe the equilibrium non-convergent ordering process in MgFe (sub 2) O (sub 4) , and they both fit the data well.