Structural Studies and Thermal Analysis in the Cs₂MoO₄-PbMoO₄ System with Elucidation of -Cs₂Pb(MoO₄)₂

The quaternary compound Cs2Pb(MoO4)(2) was synthesized and its structure was characterized using X-ray and neutron diffraction from 298 to 773 K, while thermal expansion was studied from 298 to 723 K. The crystal structure of the high-temperature phase beta-Cs2Pb(MoO4)(2) was elucidated, and it was found to crystallize in the space group R (3) over barm (No. 166), i.e., with a palmierite structure. In addition, the oxidation state of Mo in the low-temperature phase alpha-Cs2Pb(MoO4)(2) was studied using X-ray absorption near-edge structure spectroscopy. Phase diagram equilibrium measurements in the Cs2MoO4-PbMoO4 system were performed, revisiting a previously reported phase diagram. The equilibrium phase diagram proposed here includes a different composition of the intermediate compound in this system. The obtained data can serve as relevant information for thermodynamic modeling in view of the safety assessment of next-generation lead-cooled fast reactors.