Phase Diagram and Pressure Effects on Transport Properties of BaCo_{1-cursive Greek chi}Ni_{cursive Greek chi}S₂

Transport measurements under the hydrostatic pressure p up to 18.8 kbar have been carried out on single crystals of BaCo_{1-cursive Greek chi}Ni_{cursive Greek chi}S₂, which has a layered structure and exhibits the Mott metal-insulator (M-I) transition both with varying cursive Greek chi and with applying pressure. Based on resistivity data for cursive Greek chi = 0.00, 0.05. 0.14 and 0.18, a T-p-cursive Greek chi phase diagram of BaCO_{1-cursive Greek chi}Ni_{cursive Greek chi}S₂ has been constructed. The phase diagram is similar to that of (V_{1-cursive Greek chi}M_{cursive Greek chi})₂O₃ (M=Ti and Cr), although the present system does not exhibit clear discontinuity of the transition. Detailed transport behavior observed near the M-I transition induced by the external pressure are presented. For cursive Greek chi = 0.00, where a large Mott energy gap exists at ambient pressure, the intrinsic critical behavior of the Mott M-I transition seems to be observed, while for the samples with cursive Greek chi ≠ 0, randomness effects caused by the Ni-substitution for Co seems to be reflected in the critical behavior.