Quasielastic Mössbauer spectroscopy and quasielastic neutron scattering from non-Bravais lattices with differently occupied sublattices

We present the full theory for the quasielastic line broadening in Mössbauer spectroscopy and incoherent neutron scattering, caused by atomic jumps in a non-Bravais lattice, the sublattices of which are differently occupied. As a demonstration, the theory is applied to two cases that have been studied experimentally: iron diffusion in cubic ${\mathrm{Fe}}_{65}$ ${\mathrm{Al}}_{35}$, an ordered B2 (CsCl) structure (examined by Mössbauer spectroscopy), and nickel diffusion in hcp ${\mathrm{Ni}}_{53}$ ${\mathrm{Sb}}_{47}$, an ordered B8 (NiAs) structure (incoherent neutron scattering).