Structural transition and doping induced superconductivity in IrTe$_2$*

Doped IrTe$_2$ compounds are of current interest as they offer the opportunity to investigate the relationship between a structural transition and the appearance of superconductivity. Here we present the results of an investigation of the structural transition of Ir$_{1-x}$Pt$_x$Te$_2$ (x=0, 0.03, and 0.05) by X-ray and neutron diffraction. In IrTe$_2$ a structural modulation was observed with a wave vector of $k$ = (1/5, 0, 1/5) below 285 K, accompanied by a structural transition from a trigonal to a triclinic lattice. First principles calculations suggest the local bonding instability associated with the Te 5$p$ states is likely the origin of the structural phase transition. Pt-doping (x=0.03) suppresses the structural transition down to 70 K and the superconductivity appears at 3 K. No response to onset of superconductivity was observed in the structural parameters suggesting that strong electron-lattice coupling does not play a role in IrTe$_2$.