Doping effect on the structure and physical properties of quasi-one-dimensional compounds Ba₉Co₃(Se_1-xS_x)₁₅ (x = 0-0.2)

A series of samples of Ba₉Co₃(Se_1-xS_x)₁₅ (x = 0, 0.05, 0.1, 0.15, 0.2) with quasi-one-dimensional (1D) structure were successfully synthesized under high-temperature and high-pressure conditions. The influence of partial substitution of S for Se on the structure, electronic transport, and magnetic properties of Ba₉Co₃(Se_1-xS_x)₁₅ has been investigated in detail. The x-ray diffraction data shows that the lattice constant decreases linearly with increasing S-doping level, which follows the Vegrad's law. The doped S atoms preferentially occupy the site of Se atoms in CoSe₆ octahedron. Physical properties measurements indicate that all the samples of Ba₉Co₃(Se_1-xS_x)₁₅ are semiconducting and display spin glass behavior. As the replacement of Se by smaller size S, although the inter-chain distance decreases, the electronic hopping between CoSe/S₆ chains is weakened and leads to an increase of band gap from 0.75 eV to 0.86 eV, since the S-3p electrons are more localized than Se-4p ones. Ba₉Co₃(Se_1-xS_x)₁₅ exhibits 1D conducting chain characteristic.