Sphaleritelike vibration mode in chalcopyrites

Zone-centered phonons of chalcopyrite crystals were examined and it was found that the energies of the highest-frequency $B_2$- and $E$-mode phonons coincide. These coincident phonons obey empirical correlations similar to those followed by zone-centered phonons of sphalerite crystals: (i) ${\nu }_{\mathrm{TO}}^2\propto \frac{1}{\mu }$, (ii) ${\nu }_{\mathrm{LO}}^2\propto \frac{1}{\mu }$, (iii) $\frac{({\nu }_{\mathrm{LO}}-{\nu }_{\mathrm{TO}})}{{\nu }_{\mathrm{TO}}}\propto q^{*}$, and (iv) ${\left(\frac{{\nu }_{\mathrm{TO}}}{{\nu }_{\mathrm{LO}}}\right)}^2\propto q^{*2\mathrm{}}$. These characteristic relations for II-IV-${\mathrm{V}}_2$ and I-III-${\mathrm{VI}}_2$ chalcopyrites are quantified and compared with those of binary sphalerite crystals.