  The IrTe2 transition metal dichalcogenide undergoes a series of structural
and electronic phase transitions when doped with Pt. The nature of each phase
and the mechanism of the phase transitions have attracted much attention. In
this paper, we report scanning tunneling microscopy and spectroscopy studies of
Pt doped IrTe2 with varied Pt contents. In pure IrTe2, we find that the ground
state has a 1/6 superstructure, and the electronic structure is inconsistent
with Fermi surface nesting induced charge density wave order. Upon Pt doping,
the crystal structure changes to a 1/5 superstructure and then to a
quasi-periodic hexagonal phase. First principles calculations show that the
superstructures and electronic structures are determined by the global chemical
strain and local impurity states that can be tuned systematically by Pt doping.
