XAFS studies of local atomic structure of niobium tellurides

We present XAFS (K-edge) studies of the local atomic structure around the Nb and Te ions in niobium tellurides (NbTe₂, Nb₃Te₄ and NbTe₄) in comparison with ZrTe₂. Using a multi-shell best-fit analysis procedure, we have reconstructed local environments of the Nb and Te ions and compared them with the existing structural models. We found that at the Nb K-edge the XAPS data of NbTe₄ are extremely sensitive to metal clustering and to the subsequent departure from the average crystallographic positions. Moreover, at Te K-edge the XAFS data allowed us to distinguish the different type of Te-Te bonds, for instance: the dimer (Te-Te: 2.9 Å) and the squares (Te-Te: 3.3 Å) in NbTe₄, the interlayer and intralayer (Te-Te: 2.9-4.0 Å) in NbTe₂, through their Debye-Waller characteristics. In addition, a comparative analysis of Debye-Waller factors obtained in the different coordination shells (Te-Te, Te-Nb, Nb-Te and Nb-Nb) shows an evidence of correlation in the vibrational motion.