A Neutron Diffraction Study on Gallium‐Substituted Magnetite

The distribution of Ga 3+ and Fe 3+ ions in tetrahedral and octahedral sites, A and B, of the inverted spinel Fe 3−t Ga t O 4 , with t = 0.442 and 0.628 is determined from neutron diffraction measurements on two synthetic single crystals. To avoid a great extinction effect the crystals are cut into small cylindrical fragments. The extinction correction coefficients are found by a graphical method using the extinction formula I c = I o ( A + B I c ). Because of the similarity of the nuclear scattering length of Ga 3+ and Fe 3+ the distribution of the ions is found only from the magnetic reflections. By applying a magnetic field in the direction of the scattering vector, it is possible to separate the magnetic from the nuclear scattering. The Ga 3+ ions are found to be distributed between the two sites as follows: 93 and 76% in the tetrahedral, 7 and 24% in the octahedral site for the two crystals, respectively. A least square refinement of the corrected nuclear data yields agreement factors R = 0.03 and 0.04; the resulting oxygen parameters u = 0.369 ∓ 0.0006 and 0.369 ∓ ∓ 0.0008, respectively, indicate the usual shift for the inverted spinel from the ideal value 3/8.