Effective charge and ionicity in Cd1-xMnxTe.

Infrared phonon data yield effective charges and hence ionicities of the Cd-Te and Mn-Te bonds for nearly the full range of bulk zinc-blende ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te (x=0 to 0.64) and for hexagonal MnTe. The infrared ionicity for the mixed crystal agrees with recent pressure measurements except for a small x dependence, but is apparently anomalous for MnTe. In the mixed crystal the Mn-Te effective charges do not approach zero with x, suggesting that d-band effects appear.