Metal–Insulator Transition in Doped Barium Plumbates

Solid solutions in the Ba(Pb1−xSrx)O3−z system were prepared by aliovalent substitution of Pb4+ by Sr2+ ions to investigate the effect of cation stoichiometry on thermal and electrical properties as x was varied between 0 and 0.4, in the temperature range 300–523 K. The starting compound, barium plumbate (BaPbO3), has a perovskite structure and is known to exhibit metallic conductivity due to an overlap of the O2p nonbonding and the Pb–O spσ antibonding band, which is partially filled by the available electrons. The large difference in the ionic radii between the Pb4+ and Sr2+ ions introduces significant strain into the (Pb/Sr)O6 octahedra of the perovskite structure. Additionally, charged defects are created on account of the different oxidation states of the Pb4+ and Sr2+ ions. Evidence of a metal to insulator transition (MIT) of the Mott–Hubbard type has been observed at a critical concentration of Sr2+ ions.