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 stru ctures, 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 t he structures. It is shown that the proportion of metal atom sites with oct ahedral surrounding, f(oct), is linearly related to q. (C) 2001 Academic Pr ess.