The oxygen-deficient perovskite [formula omitted] —A p-type semi-conductor with high Cu(III) and fe(IV) contents

Abstract

A novel oxygen-deficient perovskite Ba 0.5La 0.5Fe 1 − xCu xO 2.75 − x 2 + δ has been synthesized. The structural characteristics of this cubic phase were established by X-ray diffraction and electron diffraction. The chemical analysis coupled with the Mossbauer spectroscopy and the magnetic susceptibility measurements allowed the different oxidation states of iron and copper to be determined according to the general formula: Ba 0.5La 0.5Fe (1 − x)(1 − y) IIIFe (1 − x)y IVCu x(1 − z) IICu xz III0 2.75 − x 2 + δ . An interesting feature deals with the high Fe(IV) and Cu(III) contents in those oxides 0.26 ⩽ y⩽ 0.49 and 0.19 ⩽ z ⩽ 0.44. The octahedral environment of Cu(III), Fe(III) and Fe(IV) has been deduced from the Mossbauer parameters in agreement with the location of oxygen vacancies near Cu(II), leading for this latter ion to a pyramidal or square planar coordination. The electron transport properties of this oxygen-deficient perovskite are characterized by a large increase of conductivity as soon as 10% of copper is introduced in the lattice. The evolution of the conductivity and thermoelectric power of this p-type conductor versus temperature is interpreted in terms of a hole delocalization in a copper band.