Weak coupling BCS-like superconductivity in the pnictide oxide Ba$_{1-x}$Na$_{x}$Ti$_{2}$Sb$_{2}$O

We report the results of low-temperature heat capacity measurements of the pnictide oxide superconductor BaTi$_{2}$Sb$_{2}$O and the optimally Na-doped compound Na$_{0.15}$Ba$_{0.85}$Ti$_{2}$Sb$_{2}$O. 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, possibly mediated by electron-phonon interaction. The results are discussed with regard to and compared with recent first-principles calculations.