Order–Disorder Phase Transitions in Fe81Ga19–RE Alloys (RE = Dy, Er, Tb, Yb) According to Neutron Diffraction Data

Abstract—New data on the phase compositions and structural transformations in a number of Fe81Ga19 alloys doped with trace amounts (≤0.2 at %) of rare earth elements are presented. The data were obtained in neutron diffraction experiments performed with high resolution and in a continuous temperature scanning mode under heating to 900°C and subsequent cooling. It has been established that structural rearrangements generally proceed in an identical manner both in the original Fe81Ga19 alloy and in its doped analogues. Slow heating and subsequent cooling of the alloys (at a rate of ±2°C/min) leads to the formation of clusters of the D03 phase with sizes in the range of 200–300 Å in the matrix of the disordered A2 phase. The sizes and volume fraction of clusters (~0.3 of the sample volume) weakly depend on a specific composition. The degree of ordering of the atomic structure of clusters changes with temperature according to a phase transition of the second kind and is close to unity at room temperature. The search for structural ordering corresponding to the modified D03 phase, which was discovered in a number of electron-diffraction studies, did not lead to a positive result.