TiK XANES in superconducting LiTi₂O₄and related compounds

The mixed valence spinel Li1+xTi2-xO4 (O>or=x>or=0.33) compounds are superconducting for x<or=0.12 (Tcmax approximately=12.7 K) and present a metal or semiconductor-like transition for x approximately=0.2. In order to study the context of such interesting electronic properties, the authors performed TiK edge measurements in these compounds and in the related systems MgTi2O4 and TiO2. The evolution of the intensity, position and shape of the pre-edge and main edge features is reported. They show that these data do not support a one-electron description and suggest that LiTi2O4 is a correlated d electron metal (U approximately=W). Modifications in the pre-edge spectra as a function of temperature have been observed for LiTi2O4, Li1.33Ti1.67O4 and TiO2. They discuss possible interpretations of this effect (vibronic coupling or thermally induced lattice deformation).