Weak coupling BCS-like superconductivity in the pnictide oxide Ba1 _-xNa^xTi²Sb²O (x=0 and 0.15)

We report the results of low-temperature heat capacity measurements of the pnictide oxide superconductor BaTi²Sb²O doped with sodium. The temperature- and field-dependent heat capacity data are well described by a single-gap BCS theory. The estimated values for the normal-state Sommerfeld constant, the heat capacity jump at T_c, and the electron-phonon coupling constant are in favor of a conventional weak coupling superconductivity mediated by electron-phonon interaction. The results are discussed with regard to and compared with recent first-principles calculations.