Na4CrNi(PO4)3 orthophosphate powder was prepared from acid solutions of NiO, Na2CO3 and aqueous solutions of Cr(NO3)3.9H2O, and (NH4)2HPO4 at a final temperature of 750 °C. The hexagonal unit cell parameters were determined to be ah≈8.789 Å and ch≈21.481 Å in space group R3¯c. These parameters were compared to those of Na4AA′(PO4)3 (AA′=CrMg, CrCo, TiNa, ZrNa). The linear variations of these parameters versus the mean A cation radius (rAA′) are consistent with the atomic distribution found for the structure of Na4NiCr(PO4)3. The ah and ch parameters are functions of the An+ ion size.
