Investigation of the normal and superconducting states of Ba$_x$Na$_{1-x}$Ti$_2$Sb$_2$O (0 $\geq$ x $\geq$ 0.33) : a pnictide oxide compound with hole doped titanium-oxygen layers

The interest in layered transition metal oxides/pnictides was re-ignited by the discovery of the iron pnictides; 2 such as examples are, Na$_2$Ti$_2$Pn$_2$O and BaTi$_2$As$_2$O. Both compounds are comprised of a layered structure and exhibit a SDW/CDW, similar to the iron pnictide parent compounds. It is well established that by suppressing the SDW, superconductivity emerges in pnictides; therefore, can a similar approach be used for these titanium based pnictide oxides? To date, the lowering of the critical temperature for the SDW/CDW has been reported, but no superconductivity was seen for BaTi$_2$As$_2$O. We report the effects of hole doping on BaTi$_2$Sb$_2$O and its influence on the SDW and superconducting states. Initial findings from neutron scattering will also be discussed. Our parent compound, which is similar to the BaTi$_2$As$_2$O in structure, shows a SDW/CDW at 57 K. A systematic lowering of the critical temperature is seen for the SDW/CDW with increased doping. In addition, the superconducting temperature increases up to 6 K. The phase diagram as a function of doping is derived from the normal and superconducting states of the system. The lowering of the critical temperature of the SDW/CDW seems to be the key for the emergence of superconductivity.