Non-stoichiometric Compound - Defects Vs Non-stoichiometry

Defects Vs Non-stoichiometry

The cuprate superconductors highlight the concept of "defect" structures, which is related to non-stoichiometry. YBa₂Cu₃O_7−x can be viewed as a variant of the perovskite family of materials, which have idealized stoichiometry ABO₃. For the cuprates, Y + Ba occupy "A sites" whereas Cu occupies the "B sites". The non-defect material would have the stoichiometry YBa₂Cu₃O₉. Using this way of describing a structure, W₄₀O₁₁₈ is said to be a defect variant of WO₃.