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The phase diagram of the semiconductor-metal and antiferromagnetic transitions in 5 at.% Co- and 7 at.% Co-doped NiS2 is determined from the electrical resistance measurements below room temperature to 77 K at pressures up to 35 kbar. It is indicated that the antiferromagnetic transition occurs in both semiconducting and metallic phases.

TaS3 exhibits the metal-semiconductor transition at 218 K due to the Peierls instability. The electrical resistance was measured under pressure. It was found that both the transition temperature, Tp, and the activation energy at T=0 K, △(0), decrease with pressure at the rates of dTp dP ⋍-1.3 K kbar and d△(0) dP ⋍-4 K kbar , respectively, while the ratio, △ (0) Tp , is independent of pressure.

Both antiferromagnetic (TN) and weak ferromagnetic (Tc) transition temperatures of NiS2 have been measured under pressure up to 18.4 kbar. Values of dTN/dP=(0.9 ± 0.1) deg/kbar and dTc/dP=(0.4 ± 0.1) deg/kbar are obtained. The present results allow estimates of the magnetic Gruneisen constant γm = - d ln TN/d ln V of (26±5) and of the entropy change of (1.4±0.5) J/mol·deg at the first order transition temperature Tc.

The electrical resistivity measurements were made from 4.2 K to room temperature on 7 at.% Co-doped NiS 2 at pressures from 19 to 71 kbar. T 2 -dependence of electrical resistivity due to the spin fluctuations was found, and the pressure dependence of its coefficient was determined.

A semiconductor-metal transition in the electrical resistance of NiS 2 , which has been suggested to be a Mott transition, is observed with decreasing temperature under pressure up to 44 kbar. The transition temperature increases with pressure with a slope of dT dP = 6 ± 1 K/kbar . The activation energy in a semiconducting region is found to decrease with increasing pressure and to vanish at about 46 kbar. The critical pressure and temperature are predicted to be 46 ± 2 kbar and 350 ± 20 K.