  Jump frequencies of 111In/Cd tracer atoms were measured for a series of
layered phases LanCoIn3n+2 using the technique of perturbed angular correlation
of gamma rays (PAC). The frequencies were determined by analysis of nuclear
quadrupole relaxation produced by fluctuating electric field gradients. Samples
were synthesized having nominal values n= 1, 2, 3, 5 and \infty, with n=\infty
corresponding to the L12 phase LaIn3. The phases form heuristically from LaIn3
by replacing every (n+1)th (100) mixed plane of La and In atoms with a plane of
Co-atoms. For the n=1 phase, LaCoIn5, jump frequencies were too small to
detect. Two signals were observed, one for indium atoms next to the Co-planes
and the other for more distant indium atoms. No relaxation was observed for
atoms next to the Co-planes, indicating that there is no diffusion across the
Co-planes. With increasing n, jump rates for the other In-atoms increased
toward values observed for LaIn3. Jump frequency activation enthalpies for n= 3
and 5 were observed to be the same as for n=\infty, suggesting the same
diffusion mechanism. However, the jump-frequency prefactors were found to be
smaller for small n, which is attributed to reductions in the connectivity of
the diffusion sublattice. We conclude that diffusion in the layered phases is
remarkably similar to diffusion in LaIn3 once the reduced connectivity is taken
into account.
