Origin of the phase transition in IrTe₂: Structural modulation and local bonding instability

We used x-ray and neutron diffraction to determine the low-temperature structure of IrTe₂. A structural modulation was observed with a wave vector of k=(1/5,0,1/5) below T_s≈285 K, accompanied by a structural transition from a trigonal to a triclinic lattice. We also performed first-principles calculations for high-temperature and low-temperature structures, which elucidate the nature of the phase transition and the low-temperature structure. A local bonding instability associated with the Te 5p states is likely the origin of the structural phase transition in IrTe ₂.