Title: PHONON SPECTRA NEAR METAL-INSULATOR PHASE TRANSITION IN LI$_{1+X}$TI$_{2-X}$O$_{4}$ SYSTEM
Authors: E.P.Buletsa, O.F.Ivanyas, V.J.Kindrat, I.I.Nebola, I.M.Shkirta, A.J.Shtejfan (Uzhgorod National University, 46 Pidhirna Str., Uzhgorod, 88000 Ukraine)

The phonons of two end members of Li$_{1+x}$Ti$_{2-x}$O$_{4}$ spinel system, i.e., the metallic LiTi$_{2}$O$_{4}$ and the insulating Li$[$Li$_{1/3}$Ti$_{5/3}]$O$_{4}$, are calculated in superspace symmetry approach using a short-range force constant model. The composition dependence of zone-centre optical phonons in Li$_{1+x}$Ti$_{2-x}$O$_{4}$ near phase transition and Li$_{1-x}$Mg$_{x}$Ti$_{2}$O$_{4}$ has been investigated using different models of substitution. One- and two-mode behavior is therefore predicted for F$_{\textrm{1u}}$ and F$_{\textrm{2u}}$ modes in case of tetrahedral and octahedral substitution, respectively.

Key words: superspace symmetry, phonon spectra, spinel, Li$_{1+x}$Ti$_{2-x}$O$_{4}$
PACS: 61.50.Ah, 63.