Moser's C-line, the apparent multiplicity m′ and modules in descriptions of L-Ta2O5 and related structures

Several L-Ta2O5 related phases, often classified as type I and type II structures, are described as composed of elements of alpha- and beta -U3O8 type. Published powder patterns are reindexed in a four-index notation using a modulation vector q = qb*. From the so-called C-line a relation between the apparent multiplicity m' and q is obtained: m' = 1/\2-3q\. A modified (AB) module based on the alpha -U3O8 structure, is given and used in modeling the structures. It is shown that the proportion of metal atom sites with octahedral surrounding, f(oct), is linearly related to q. (C) 2001 Academic Press.