Structure and properties of M/sup I/M/sub 2//sup IV/(PO/sub 4/)/sub 3/ in quadrivalent actinoid phosphates

A survey is presented on the crystallographic and IR features of double actinoid-alkali phosphates of the form M/sup (I)/M/sub 2//sup (IV)/ (PO/sub 4/)/sub 3/; it is found that the compounds Li/sup -/, Na/sup -/, K/sup -/, Rb/sup -/, CsTh/sub 2/(PO/sub 4/)/sub 3/, Li/sup -/, Na/sup -/, KU/sub 2/(PO/sub 4/)/sub 3/, NaNp/sub 2/(PO/sub 4/)/sub 3/ have monoclinic structures and form an isostructural series. Double salts do not occur in the uranium-rubidium and uranium-cesium systems. Sodium plutonium phosphate is orthorhombic, which indicates a morphotropic transition in the NaM/sub 2//sup (IV)/ (PO/sub 4/)/sub 3/ series at the Np-Pu boundary. Some regularities have been established in the structures and effects of M/sup (I)/ and M/sup (IV)/.