Low‐Temperature Hydrothermal Synthesis of PbUO ₄

ABSTRACT

Lead uranate (PbUO ₄ ) is a ternary uranium (VI) oxide with significant relevance to actinide ceramic materials, often prepared via traditional high‐temperature solid‐state or flux‐based synthesis methods. Herein, a low‐temperature hydrothermal route to phase‐pure orthorhombic PbUO ₄ is demonstrated. PbUO ₄ was synthesized via reaction of synthetic metaschoepite (UO ₃ ·nH ₂ O) with Pb(NO ₃ ) ₂ under hydrothermal conditions at temperatures as low as 150°C–180°C. Systematic variation of solution pH, temperature, and reaction time shows that PbUO ₄ formation is strongly pH‐dependent, with lower pH favoring layered Pb‐U oxide hydrate intermediates and higher pH (≈4.5) enabling direct PbUO ₄ crystallization over a broad temperature window. Powder x‐ray diffraction confirms phase purity, while optical and scanning electron microscopies reveal distinct, tunable PbUO ₄ morphologies ranging from prism‐like to block‐like crystals. Thermogravimetric analysis shows that hydrothermally synthesized PbUO ₄ is stable in air to temperatures exceeding 1000°C. These results establish hydrothermal synthesis as a low‐energy route to PbUO ₄ and highlight solution chemistry as a key parameter for controlling ternary uranium oxide ceramic formation.