Raman scattering, superconductivity, and phonon density of states of stoichiometric and nonstoichiometric TiN

Raman scattering and superconductivity of titanium nitride with various N deficiencies have been investigated. While in stoichiometric superconducting TiN second-order Raman scattering is predominant, first-order Raman scattering increases with increasing N deficiency. The first-order Raman spectrum which agrees well with the phonon density of states shifts to higher frequencies when the N deficiency grows. This frequency shift is particularly strong at small N deficiencies (∼5%) and is coupled with a drastic drop of $T_c$. The shift of the phonon density of states indicates phonon anomalies in stoichiometric TiN at 200 ${\mathrm{cm}}^{-1\mathrm{}}$ in close agreement with just performed neutron studies. In almost stoichiometric TiN the mean-square frequencies $〈{\omega }^2〉$ from the Raman spectra are in good agreement with corresponding specific-heat data. The similarities between the nonstoichiometric Ti${\mathrm{N}}_{0.55}$ and TiC are discussed.