Perovskite structure oxygen deficient

The magnetic properties of the new solid solution series SrFe Rui 3 3, (0 < X < 0.5) with distorted perovskite structure, where iron substitutes exclusively as Fe(in) thereby causing oxygen deficiency, has also been studied by Greenwood s group [147] using both u and Fe Mossbauer spectroscopy. Iron substitution was found to have little effect on the magnetic behavior of Ru(IV) provided that X remains small (x < 0.2). 

The most important of these are perovskite structure solids with a formula A2+b4+o3 that can be typified by BaCeC>3 and BaZrCV The way in which defects play a part in H+ conductivity can be illustrated by reference to BaCeCV BaCeC>3 is an insulating oxide when prepared in air. This is converted to an oxygen-deficient phase by doping the Ce4+ sites with trivalent M3+ ions (Sections 8.2 and 8.6). The addition of the lower valence ions is balanced by a population of vacancies. A simple substitution reaction might be formulated ... 

Perovskites constitute an important class of inorganic solids and it would be instructive to survey the variety of defect structures exhibited by oxides of this family. Nonstoichiometry in perovskite oxides can arise from cation deficiency (in A or B site), oxygen deficiency or oxygen excess. Some intergrowth structures formed by oxides of perovskite and related structures were mentioned in the previous section and in this section we shall be mainly concerned with defect ordering and superstructures exhibited by these oxides. 

A significant step in the history of the HTSs was the discovery in 1966 of superconductivity in the oxygen-deficient perovskite SrTi03 5, containing some barium or calcium substituted for strontium. Although the Tc value was very low (0.55 K), in retrospect it can be seen as the first superconducting ceramic. In 1979 a Tc of approximately 13 K was discovered for BaPb075Bi025O3, which also has the perovskite structure. 

Partial substitution of A and B ions is allowed, yielding a plethora of compounds while preserving the perovskite structure. This brings about deficiencies of cations at the A-or B-sites or of oxygen anions (e.g. defective perovskites). Introduction of abnormal valency causes a change in electric properties, while the presence of oxide ion vacancies increases the mobility of oxide ions and, therefore, the ionic conductivity. Thus, perovskites have found wide apphcation as electronic and catalytic materials. 

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