Raman scattering from the filled tetrahedral semiconductor LiZnP

The bonding character in the filled tetrahedral semiconductor LiZnP (space group: F4¯3m), viewed theoretically as a zinc-blende-like (ZnP${)}^{\mathrm{-}}$ lattice partially filled with He-like ${\mathrm{Li}}^{+}$ interstitials, was studied using a Raman-scattering method. Two longitudinal-optical (LO) and transverse-optical (TO) phonons at k∼0 (Γ point) for Li-P and Zn-P pairs were observed at 421 and 363 ${\mathrm{cm}}^{\mathrm{-}1}$ and 265 and 230 ${\mathrm{cm}}^{\mathrm{-}1}$, respectively. In comparison with the separation of the LO and TO branches at k∼0 for each pair, the Li-P bond appears to have relatively high ionicity, whereas the force constant of Zn-P is about 50% higher than that of Li-P, showing the relatively high covalency of Zn-P bond. These results are also supported by the fact that the macroscopic transverse effective charge ${\mathit{e}}_{\mathit{T}}^{\mathrm{*}}$ of the Zn-P bond is larger than that of the Li-P bond.