Fig. 1. (a) Electrical resistivity of BaIr₂Ge₇ as a function of temperature at various pressures in run I. (b) and (c) Temperature-dependent resistivity of BaIr₂Ge₇ in the vicinity of the superconducting transition. Temperature dependence of resistivity under different magnetic fields for BaIr₂Ge₇ at 3.8 (d) and 44.9 GPa (e), respectively. (f) Estimated upper critical field for BaIr₂Ge₇. Here, T_c is determined as a 90% drop in the normal-state resistivity. The solid lines represent fits based on the Ginzburg–Landau (G-L) formula.

Fig. 2. (a) Electrical resistivity of Ba₃Ir₄Ge₁₆ as a function of temperature at various pressures in run I. (b) Temperature-dependent resistivity of Ba₃Ir₄Ge₁₆ in the vicinity of the superconducting transition. (c) Temperature dependence of resistivity under different magnetic fields for Ba₃Ir₄Ge₁₆ at 2.0 GPa. (d) Pressure-dependent resistivity at 300 K and T_c of Ba₃Ir₄Ge₁₆.

Fig. 3. (a) Crystal structures of BaIr₂Ge₇ and Ba₃Ir₄Ge₁₆. Polyhedra of different colors stand for distinct cages. (b) XRD patterns collected at various pressures for BaIr₂Ge₇ with an x-ray wavelength λ = 0.6199 Å (background-subtracted). (c) Selected Raman spectra at various pressure for BaIr₂Ge₇.

Fig. 4. Pressure dependences of (a) the superconducting transition temperatures T_c, (b) the resistivity at 300 K and the experimental volume relative to the Ammm phase, and (c) selected Raman shifts for BaIr₂Ge₇. The values of T_c were determined from the high-pressure resistivity.

Table 1. Structure and superconducting properties of BaIr₂Ge₇ and Ba₃Ir₄Ge₁₆.