Elastic anisotropy and phonon focusing in NiAl: Atomic study

The sets of the slowness surface of NiAl, longitudinal (L) for the inner sheet, fast transverse (FT) for the middle, and slow transverse (ST) for the outer; The section with large Gaussian curvature on the slowness surface indicates a “defocusing” of group-velocity vectors, or a reduction in phonon flux for the corresponding propagation directions.