  In a pressure-temperature (P-T) diagram for synthesizing IrTe2 compounds, the
well-studied trigonal (H) phase with the CdI2-type structure is stable at low
pressures. The superconducting cubic (C) phase can be synthesized under higher
temperatures and pressures. A rhombohedral phase with the crystal structure
similar to the C phase can be made at ambient pressure; but the phase contains
a high concentration of Ir deficiency. In this paper, we report that a rarely
studied monoclinic (M) phase can be stabilized in narrow ranges of pressure and
temperature in this P-T diagram. The peculiar crystal structure of the M-IrTe2
eliminates the tendency to form Ir-Ir dimers found in the H phase. The M phase
has been fully characterized by structural determination and measurements of
electrical resistivity, thermoelectric power, DC magnetization, and specific
heat. These physical properties have been compared with those in the H and C
phases of Ir1-xTe2. Moreover, magnetic and transport properties and specific
heat of the M-IrTe2 can be fully justified by calculations with the
density-functional theory presented in this paper.
