The synthesis mechanism of CsCaNd(PO4)(2) from nitrates, carbonates and oxides of the different cations was investigated with the aim of immobilizing cesium. Two transitory phases, a monazite-type one, NdPO4, and a poorly crystallized cesium phosphate, CsCaPO4, were proposed to explain the formation of CsCaNd(PO4)(2). Direct synthesis from NdPO4 and CsCaPO4 was thus carried out. It allowed to underline that within a 900-1000 degrees C temperature range the rhabdophane structure, CsCaNd(PO4)(2), was formed. However, the reaction was also found to be incomplete and this was assumed to be due to a lack of reactivity in concern with the high stability of monazite. (c) 2005 Published by Elsevier B.V.