Determination of the metal ordering in meteoritic (Fe,Ni)₃P crystals

Synchrotron radiation diffraction studies of meteoritic (Fe,Ni)₃P crystals have been performed to reveal the ordering of the elements Fe and Ni on the three metal sites M1, M2 and M3 of the unit cell. The δ synthesis technique, which is a two-wavelength method using anomalous dispersion effects, was applied. For (Fe,Ni) phosphide crystals with different Fe:Ni ratios extracted from different meteorites, it was found that Ni occupies the M3 site and also partially the M2 site, avoiding the M1 position, whereas the M1 site is preferentially occupied by Fe. In connection with earlier results known from the literature, this metal distribution seems to be characteristic of this compound, and is independent of thermodynamic formation conditions.