Absence of structural transition in M_0.5IrTe₂ (M = Mn, Fe, Co, Ni)

M-doped IrTe₂ (M = Mn, Fe, Co, Ni) compounds were synthesized by solid-state reaction. Single crystal x-ray diffraction experiments indicate that part of the doped M ions (M = Fe, Co, and Ni) substitute for Ir, and the rest intercalate into the octahedral interstitial sites located in between IrTe₂ layers. Due to the lattice mismatch between MnTe₂ and IrTe₂, Mn has limited solubility in IrTe₂ lattice. The trigonal structure is stable in the whole temperature range 1.80 K≤ T ≤ 300 K for all doped compositions. No long-range magnetic order or superconductivity was observed in any doped compositions above 1.80 K. A spin glass behavior below 10 K was observed in Fe-doped IrTe₂ from the temperature dependence of magnetization, electrical resistivity, and specific heat. The low temperature specific heat data suggest the electron density of states is enhanced in Fe- and Co-doped compositions but reduced in Ni-doped IrTe₂. With the 3d transition metal doping the trigonal a-lattice parameter increases but the c-lattice parameter decreases. Detailed analysis of the single crystal x-ray diffraction data shows that interlayer Te-Te distance increases despite a reduced c lattice. The importance of the Te-Te, Te-Ir, and Ir-Ir bonding is discussed.