Chemical and hydrostatic pressure induced metallization in $$\hbox {NiS}_{2-x}$$ $$\hbox {Se}_x$$ single crystals

External control parameters such as pressure, chemical substitution, and temperature play a central role in tuning the electronic states of strongly correlated systems. We investigate the insulator-to-metal transition (MIT) in [Formula: see text] [Formula: see text] by combining hydrostatic and chemical pressures across a broad composition range ([Formula: see text]). Pure [Formula: see text] shows a systematic shift of the weak ferromagnetic transition temperature under pressure. Metallization occurs at a relatively low pressure (1.3 kbar) for [Formula: see text] [Formula: see text], whereas lightly doped [Formula: see text] [Formula: see text] requires higher pressure. At [Formula: see text], a metallic state emerges solely from chemical substitution without external pressure. These results demonstrate that Se substitution is more efficient than hydrostatic pressure in promoting metallization, though we note that chemical substitution modifies not only the lattice parameter but also covalency and p-d hybridization, and is therefore not strictly equivalent to external compression. A unified pressure-doping-temperature phase diagram is constructed, providing new insights into correlation-driven MITs and offering guidance for the design of functional Mott systems.