= (La,Y), Pr]**

We report measurements of the ac magnetic susceptibility of the iron-based mixed-chalcogenide superconductor Fe_1+εTe_0.5Se_0.5, and of the electrical resistivity of doped nickel-oxide compounds R_1-xCe_xNiO₃, with R = Pr or (La,Y), over the pressure range 0–20 kbar (0–2.0 GPa). Our iron-based material is optimized (ε ≈ 0.07) for bulk superconductivity, exhibiting an ambient-pressure superconducting transition at T_c ≈ 14 K, well above the transition of bulk FeSe (T_c = 9 K). With applied pressure, we observe an immense, nearly linear increase of T_c, with dT_c /dP = +7.0±0.5 K/GPa. We have prepared bulk “113” doped nickelates using high-oxygen-pressure (150–200 bar), high-temperature (T ≈ 1000°C) synthesis. For undoped PrNiO₃, the metal insulator transition temperature decreases with pressure, with reported dT_MI/dP ≈ –42 to –76 K/GPa [1,2]. For Pr_1-xCe_xNiO₃ with x ≈ 0.0–0.2, we are exploring variations in dT_MI/dP. We consider both steric (e.g., band-broadening, bond-straightening), electron-doping, and hole-filling contributions to this behavior.
[1] X. Obradors et al., Phys. Rev. B 47 12353 (1993); [2] P. C. Canfield et al., Phys. Rev. B 47 12357 (1993).