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

Area of Science:

• Materials Science
• Solid State Chemistry
• Crystallography

Background:

• Cesium lead molybdate (Cs2Pb(MoO4)2) is a quaternary compound with potential applications.
• Understanding its structural and phase behavior is crucial for material development and safety assessments.

Purpose of the Study:

• To synthesize and characterize Cs2Pb(MoO4)2.
• To elucidate the crystal structure of its high-temperature phase.
• To investigate its thermal expansion and revise the Cs2MoO4-PbMoO4 phase diagram.

Main Methods:

• X-ray and neutron diffraction for structural characterization (298–773 K).
• Thermal expansion studies (298–723 K).
• X-ray absorption near-edge structure (XANES) spectroscopy for Mo oxidation state.
• Phase diagram equilibrium measurements.

Main Results:

• The high-temperature phase (β-Cs2Pb(MoO4)2) crystallizes in the R3̅m space group, exhibiting a palmierite structure.
• Thermal expansion was measured, providing insights into material stability.
• The Cs2MoO4-PbMoO4 phase diagram was revised, proposing a different composition for the intermediate compound.
• Mo oxidation state in the low-temperature phase (α-Cs2Pb(MoO4)2) was determined.

Conclusions:

• The study provides a comprehensive structural and phase behavior analysis of Cs2Pb(MoO4)2.
• Revised phase diagram data are essential for thermodynamic modeling.
• The findings contribute to the safety assessment of lead-cooled fast reactors.