On the crystal structures of Pr7W6.25M0.75O30 (M = Zn, Co) and so-called MPr2W2O10 (M = Co, Mn, Cd)

Abstract

Pr₇W_6.25M_0.75O₃₀ (M = Zn, Co) are shown to crystallize with a La₇Mo₇O₃₀ columnar perovskite type arrangement. Evidence is given that materials previously presented as MPr₂W₂O₁₀ (M = Mn, Co, Cd) have a Pr₇W_6.25M_0.75O₃₀ formulation with an A₇B₇O₃₀ structure. It is suggested that their properties (particularly a colossal dielectric constant) should be re-evaluated on pure samples with the right composition.