[en] The synthesis and results of the X-ray diffraction examination of complex orthophosphates involving the cations Ca²⁺, Cd²⁺, Gd³⁺, Ti⁴⁺, Hf⁴⁺, Ce⁴⁺, U⁴⁺, and Pu⁴⁺ are described. Crystalline products containing either cerium or plutonium or these two elements together were prepared. Cerium was used as plutonium simulator. Phosphates containing cations Ti⁴⁺ and Hf⁴⁺ were found to form two-phase products. One of these phases was assumed to be of the NaZr₂(PO₄)₃ (NZP) type, the other one of the CePO₄ type (monazite). Formation of single-phase products with a monazite structure was found in the specimens that did not contain Ti and Hf. X-ray diffraction characteristics of synthesised phases were identified. An effect of the cation composition on the phase formation and also the effect of the cation size on the crystal lattice parameters of the formed phases were established. (author)