Local structural displacements across the structural phase transition in IrTe 2: Order-disorder of dimers and role of Ir-Te correlations

We have studied local structure of IrTe2 by Ir L3-edge extended x-ray absorption fine structure (EXAFS) measurements as a function of temperature to investigate origin of the observed structural phase transition at Ts∼270 K. The EXAFS results show an appearance of longer Ir-Te bond length (ΔR∼0.05 Å) at T<Ts. We have found Ir-Ir dimerization, characterized by distinct Ir-Ir bond lengths (ΔR∼0.13 Å), existing both above and below Ts. The results suggest that the phase transition in IrTe2 should be an order-disorder-like transition of Ir-Ir dimers assisted by Ir-Te bond correlations, thus indicating important role of the interaction between the Ir 5d and Te 5p orbitals in this transition.