Superconductivity at 4.4 K in Ba2Bi3

We report on the superconductivity in Ba2Bi3, which contains planar anionic Bi ribbon nets with four- and three-bonded Bi separated by cationic Ba layers. A nearly single-phase sample is synthesized by reacting Ba and Bi powders at 800 degrees C under a pressure of 1 GPa. The temperature-dependent resistivity (P)(T) shows metallic behavior with a residual resistivity ratio of 27.3 and indicates a sharp superconducting transition at 4.4 K. The magnetic susceptibility has a large diamagnetic transition at a similar temperature. From the analysis of (P)(T), the Debye temperature circle times(D) and electron-phonon coupling constant lambda(o-p) are derived as 75.9 K and 1.0, respectively, indicating that Ba2Bi3 is a superconductor in the strong-coupling regime. Ba2Bi3 is a type-II superconductor with an estimated upper critical field H-c2( 0) of about 1.23 T. For increasing pressures up to 1.5 GPa, T-c linearly decreases with a slope of -0.56 K GPa(-1).