Structural and electronic properties of BaBi_1-xTl_xO₃ (0.0≤x≤0.50)

Structural and physical properties of BaBi_1-xTl_xO₃ were investigated by means of powder X-ray diffraction, electrical resistivity and magnetic susceptibility measurements. For 0.0≤x≤0.20, the compounds are monoclinic and n-type semiconductors; while for 0.40<x≤0.50, the phases are orthorhombic and p-type semiconductors. A mixed phase region of both monoclinic and orthorhombic compounds is observed at 0.20<x<0.40. The resistivity of the orthorhombic phase is about two orders of magnitude lower than that of monoclinic phase. BaBi_0.5Tl_0.5O₃, which is isoelectronic with BaPbO₃, is a single phase material with orthorhombic unit cell parameters a=6.076( 1 ) A ̊, b=6.056( 1 ) A ̊ and c=8.549( 1 ) A ̊. The monoclinic-orthorhombic structural phase transition and the concomitant variations in the physical properties of BaBi_1-xTl_xO₃ are attributed to the suppression of the charge density wave state in BaBiO₃, as a result of Tl^III substitution. Superconductivity was found at 8 K in BaBi_0.25Tl_0.25Pb_0.5O₃, which is isoelectric with BaBi_0.5Tl_0.5O₃.