The available calculated density of states of TiOz does not predict the very first weak peak at the onset of the Ti K-edge absorption spectra indicating that this feature is not simply due to a one-electron (dipole) transition. In this short paper we present a joint experimental and theoretical study of all the three weak pre-peaks at the Ti K-edge of Ti02. Our interpretation takes into account both dipole and quadrupole transitions as well as the influence of the core hole effect.

The mixed valence spinel Lil+xTi2-x04 (0 2 x 2 0.33) compounds are superconducting for x s 0.12 (T,,,, = 12.7 K) and present a metal or semiconductor-like transition for x = 0.2. In order to study the context of such interesting electronic properties, we performed Ti Kedge measurements in these compounds and in the related systems MgTi204 and TiO,.The evolution of the intensity, position and shape of the pre-edge and main edge features is reported. We show that these data do not support a one-electron description and suggest that LiTi204 is a correlated d electron metal ( U Modifications in the pre-edge spectra as a function of temperature have been observed for LiTi,O,, Lil.33Ti, 6704 and Ti02. We discuss possible interpretations of this effect (vibronic coupling or thermally induced lattice deformation).

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The temperature dependence of the pre-edge features in x-ray absorption spectroscopy is reviewed. Then, the temperature dependence of the pre-edge structure at the K-edge of titanium in rutile TiO(2) is measured at low and room temperature. The first two peaks grow with temperature. The fact that these two peaks also correspond to electric quadrupole transitions is explained by a recently proposed theory.

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