Figure 4. Chemical and physical pressure.

(a) The activation energy plot E_ρ=−k_BT²(‖lnρ/‖T) for Ta₂Ni(Se_1−xS_x)₅ that clearly shows the systematic shift of T_C with S doping. The inset shows resistivity curves (I || a axis) as a function of temperature. Triangles mark the transition temperatures for each sample. Variations in absolute values are due to uncertainties in, for example, exact sample dimensions. In b, we show the equivalent data for the Ta₂Ni(Se_1−xTe_x)₅ series. (c) The activation energy plot as a function of temperature for a single high-pressure experiment showing both the systematic reduction of E_ρ with pressure as well as the suppression of T_C. Additional data from a high-temperature run are also included. The inset shows the equivalent resistivity data with emphasis of T_C by triangles. (d) Equivalent data to c for Ta₂Ni(Se_0.8Te_0.2)₅.