Crystal chemistry of MIIM′IV(PO4)2 double monophosphates

(MM)-M-II'(IV)(PO4)(2) compounds have been extensively studied for several decades for their potential applications in the field of several domains such as matrices for actinides conditioning, phosphors etc. In this paper, the relationships between composition and crystal structure of these compounds are established. A review of the various processes used for the synthesis of these compounds is also proposed, as well as their most reported properties. (MM)-M-II'(IV)(PO4)(2) structures stem from two different archetypes: the cheralite and the yavapaiite structures, with some exceptions that are also described in this article. The ratio of the cations radii appears to be the most relevant parameter. The high ratio between the ionic radii of the divalent and tetravalent cations in yavapaiite derivates results in the ordering of these cations into well-differentiated polyhedra whereas cheralite is the only non-ordered structure encountered for (MM)-M-II'(IV)(PO4)(2) compounds. (C) 2015 Elsevier Inc. All rights reserved.