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.