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 Tc. The shift of the phonon density of states indicates phonon anomalies in stoichiometric TiN at 200 cm^-1 in close agreement with just performed neutron studies. In almost stoichiometric TiN the mean-square frequencies 〈ω²〉 from the Raman spectra are in good agreement with corresponding specific-heat data. The similarities between the nonstoichiometric TiN0.55 and TiC are discussed.