STOICHIOMETRY, PERCOLATION, AND VERWEY ORDERING IN MAGNETITE

Neutron scattering experiments on Fe3(1 - delta)O4 single crystals show that, for delta = 0, the well established additional Bragg Peaks occur at (h,0,l + 1/2), below T(V) = 122.5 K with abrupt disappearance of the diffuse planar scattering associated with 1D correlations along the cubic axis. For delta = 0.006, the superlattice peaks never become resolution limited, long-range order is not attained, and the diffuse scattering increases continuously with cooling. This composition exceeds the percolation limit beyond which the transition is inhibited by insufficient average charge per ordered unit cell.