Structural Studies and Thermal Analysis in the Cs 2 MoO 4 -PbMoO 4 System with Elucidation of β-Cs 2 Pb(MoO 4 ) 2 .

The quaternary compound Cs 2 Pb(MoO 4 ) 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 β-Cs 2 Pb(MoO 4 ) 2 was elucidated, and it was found to crystallize in the space group R 3̅ m (No. 166), i.e., with a palmierite structure. In addition, the oxidation state of Mo in the low-temperature phase α-Cs 2 Pb(MoO 4 ) 2 was studied using X-ray absorption near-edge structure spectroscopy. Phase diagram equilibrium measurements in the Cs 2 MoO 4 -PbMoO 4 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.