The infra-red absorption which was associated with localized vibrational modes in samples which contained both Li and a group-IV impurity (Si, Ge, Sn) was studied. On the basis of the experimental results, it was established that certain point defects played a dominant role. These were isolated LiCd, LiCd-Lii nearest-neighbor pairs, and LiCd-MCd next-nearest neighbor pairs, where MCd denoted Si, Ge, or Sn at a Cd site. It was also found that some localized vibrational modes of LiCd-MCd pairs were connected with the coupled motion of LiCd and MCd impurities and that the model of a weakly coupled impurity pair, which was usually used to analyze experimental results, was not applicable here.

R.Zielinska-Purgal, J.Piwowarczyk, W.Nazarewicz: Physica Status Solidi B, 1994, 186[2], 355-65