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Jump frequencies of Cd tracer atoms in In3La were measured via nuclear quadrupole relaxation caused by stochastic reorientation of the electric field gradient using the method of perturbed angular correlation of gamma rays. Activation enthalpies of 0.53(1) and 0.81(1) eV were found at the two phase boundaries, which differ in composition by only about 0.1 at. %. The jump frequency was found to be higher at the more In-rich phase boundary, ruling out a simple In-vacancy diffusion mechanism. Possible diffusion mechanisms and general applicability of the method are discussed.

In the perfect magnesium aluminate spinel structure all the tetrahedral sites are occupied by Mg2+ ions, while Al3+ ions occupy all the octahedral sites. Real MgAl2O4, however, exhibits cation disorder (inversion), so that some Mg2+ ions reside in octahedral sites with an equal number of Al3+ ions in tetrahedral sites. Atomistic simulation was used to correlate the degree of inversion with changes in lattice parameter. Results from several approaches, including a combined energy minimization–Monte Carlo technique (CEMMC), are compared with available experimental data. These show that the mean field method is not useful, while the defect volume approach can yield predictions that are useful in interpreting the CEMMC results, which agree most closely with experiment.

Using perturbed angular correlation spectroscopy, jump frequencies of Cd tracer atoms were measured for 12 indides In3(B) (B = rare earth) in paired samples having compositions at each of the opposing phase boundaries. Jump frequencies in heavy lanthanide indides were observed to be smaller for In-richer compositions than for In-poorer compositions, but greater in the light lanthanide indides. These findings signal an unmistakable change in diffusion mechanism from the simple In-sublattice vacancy mechanism for heavy lanthanides to a B-vacancy mechanism for light lanthanides.