  The interplay between superconductivity and charge density wave
(CDW)/metal-to-insulator transition (MIT) has long been interested and studied
in condensed matter physics. Here we study systematically the charge density
wave and superconductivity properties in the solid solutions Zn1-xCuxIr2-yN(N =
Al, Ti, Rh)yTe4. Resistivity, magnetic susceptibility and specific heat
measurements indicate that the CDW state was suppressed immediately while the
superconducting critical temperature (Tc) differs from each system. In the Al-
and Ti-substitution cases, Tc increase as y increases and reaches a maximum
around 2.75 K and 2.84 K respectively at y = 0.075, followed by a decrease of
Tc before the chemical phase boundary is reached at y = 0.2. Nevertheless, Tc
decreases monotonously with Rh-doping content y increases and disappears above
0.3 with measuring temperature down to 2 K. Surprisingly, in the Zn1-xCuxIr2Te4
solid solution, Tc enhances as x increases and reaches a maximum value of 2.82
K for x = 0.5 but subsequently survives over the whole doping range of 0.00 -
0.9 despite Tc changes slightly with higher doping content, which differs from
the observation of zinc doping suppressing the superconductivity quickly in the
high Tc cuprate superconductors. The specific heat anomaly at the
superconducting transitions for the representative optimal doping samples are
all slightly higher than the BCS value of 1.43 and indicate bulk
superconductivity in these compounds. Finally, the CDW transition temperature
(TCDW) and superconducting transition temperature (Tc) vs. x/y content phase
diagrams of Zn1-xCuxIr2-yN(N = Al, Ti, Rh)yTe4 have been established and
compared, which offers good opportunity to study the competition between CDW
and superconductivity in the telluride chalcogenides.
