previously, namely (M,M') = (Ni,Zn), (Ni,Co) and (Mg, Mn). Nord investigated the ordering for bimetallic tetrametaphosphates with (M,M') = (Ni,Zn), (Ni,Co), using neutron diffraction, as XRD has only small scattering factor differences between these metals. It was found that there is a slight preference for the Ni(II) ion to occupy the smaller octahedral site due to its lower ionic radius, and thus some ordering of the cations is observed. In contrast, in a recent study on MgMn(PO 3 ) 4 using XRD, no cation ordering was observed. Experimental data is presented by the A-lab for CaCo(PO 3 ) 4 , CaMn(PO 3 ) 4 and CaNi(PO 3 ) 4 .