TiK XANES in superconducting LiTi₂O₄and related compounds

Abstract

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).

Structure property relationships in the ATi2O4 (A=Na, Ca) family of reduced titanates

“…There are, in contrast, only a few reported studies of reduced valence in materials using Ti K-edge XANES. Of particular note are the works of Durmeyer et al [16] and Ra et al [17], who both studied Li 1+x Ti 2Àx O 4 (the former study included MgTi 2 O 4 and TiO 2 as reference compounds), and of Luca et al [18] who studied lithium intercalation compounds of anatase. In all cases, distinct trends in the form of the XANES signal with average titanium oxidation state were noted, and broadly similar results were seen in each study.…”

Magnetic field dependence of low-temperature specific heat of the spinel oxide superconductorLiTi2O4

“…[1][2][3][4][5][6][7][8][9][10][11] In the normal spinel-like structure (space group Fd3m) of LiTi 2 O 4 , the Li and Ti atoms are respectively at the positions of tetrahedral (8a) and octahedral (16d) sites.…”

“…Also, it is the rare oxide superconductor showing a sharp superconducting anomaly [2][3][4] in specific heat (C) in contrast to an unpronounced one in polycrystalline BaPb 1-x Bi x O 3 with a comparable T c~1 2 K. 12 The upper critical field H c2 (0) of LiTi 2 O 4 reported by several groups varied from 2 to 32.8 T. 3,7 Issues like whether the superconductivity in LiTi 2 O 4 can be well explained in the framework of BCS theory based upon the electron-phonon (e-ph) interactions and the role of the electron-electron (e-e) interactions have not been totally clearified. 9 Some theoretical predictions showed that LiTi 2 O 4 was a strong coupling BCS superconductor while the low temperature specific heat and magnetic susceptibility data implied for the conditions for weak coupling d-band superconductivity. [1][2][3][4]10 Furthermore, there has been a very recently revived debate on Anderson's resonating valance bond (RVB)-type ground state as the possible origin of superconductivity in cuprates.…”

Pre-edge structure analysis of Ti K-edge polarized X-ray absorption spectra in TiO2 by full-potential XANES calculations

“…The understanding of the chemical and electronic properties of titanium oxides is of great interest in catalysis, geological sciences, and high-To superconductivity (Kung, 1989;Farges et al, 1997, Durmeyer et al, 1990. Core level spectroscopies are known to be a good tool for such purposes and have been exploited for various titanium oxides Wu et al, 1997 and references therein).…”