Crystal chemistry of new triple-perovskite-slab intergrowth phases: non-stoichiometric barium–lead–copper mixed oxides Ba4–xPb3–xCuxO10–δ(x⩽0.33; δ⩽0.60)

Abstract

The partial substitution of Cu²⁺ for Pb⁴⁺, rather than occurring in the BaPbO₃ perovskite as claimed previously, has been identified in the triple-perovskite-slab Intergrowth plumbate Ba₄Pb₃O₁₀. New non-stoichiometric phases, barium–copper–lead mixed oxides Ba_4–xPb_3–xCu_xO_10–δ(x⩽0.33; δ⩽0.67), were prepared at 1243 K in flowing oxygen. They exhibit both barium and oxygen vacancies and Pb⁴⁺/Cu²⁺ ordering in the external perovskite layers of the triple slab, as deduced from X-ray powder structure calculations. Magnetic susceptibility measurements in the range 77–400 K point to the existence of weak ferromagnetic interactions within the perovskite slab. From the value of µ, 30% of the total Cu content is assumed to be oxidized to Cu³⁺, in agreement with the structural data. Water intercalation is characterized from crystallographic and thermal analysis. The intercalation–deintercalation process is shown to be irreversible. A similar trend with respect to water intercalation is evidenced for the double-perovskite-slab Intergrowth plumbate Ba₃Pb₂O₇.