Structure and ordering of solid solutions of iron in palladium

Abstract

Ordering of FePd alloys with compositions 75 to 95 at% Pd is studied by X-ray diffraction of multicrystalline samples in the temperature region up to 800 °C. The lattice parameter is also measured. The critical temperature for LRO in the 75 at% sample is found to be Tc = (640 ± 10) °C. No LRO is found at any other composition, but the possibility of local order in the 80at% sample exists on the basis of deviations observed in the diffuse scattering. The results support a first order reaction for LRO in the 75 at% sample. A small contraction is observed in the lattice of the 75 at% sample at disordering, in contrast with the dilatation observed in other A3B type superstructures.