Synthetic uranium oxide hydrate materials: Current advances and future perspectives

Uranium oxide hydrate (UOH) materials, a group of minerals and synthetic phases, have attracted recent attention due to their high structural flexibility and diversity as well as their primary relationship with natural weathering of the mineral uraninite and the alteration of spent nuclear fuel (SNF) in geological disposal. Due to the limited structural and chemical understanding of UOH minerals, synthetic UOH phases provide a unique opportunity to fill existing knowledge gaps through the exploration of further structural diversity and distinctive properties, as well as potential applications. Some of the latest developments of synthetic UOH phases include the incorporation of 3d transition metal and lanthanide ions, the evolution of uranyl oxide hydroxide layers driven by interlayer charge, the structural diversity of uranyl oxide hydrate frameworks, and the intrinsic driving force for the formation of diversified structural types. The purpose of this review is to provide a comprehensive summary of the latest advancements of synthetic UOH phases with 3d transition and lanthanide metal ions, including their syntheses, structural diversities, microstructures, uranium valences, vibration modes, and structural and chemical complexities. It also highlights the subsequent implications of these advancements on uranium geochemistry and SNF alterations, amongst other potential applications. A further discussion on technical challenges and knowledge gaps is included to identify areas for future research.

Flux crystal growth: a versatile technique to reveal the crystal chemistry of complex uranium oxides

This frontier article focuses on the use of flux crystal growth for the preparation of new actinide containing materials, reviews the history of flux crystal growth of uranium containing phases, and highlights the recent advances in the field. Specifically, we discuss how recent developments in f-element materials, fueled by accelerated materials discovery via crystal growth, have led to the synthesis and characterization of new families of complex uranium containing oxides, namely alkali/alkaline uranates, oxychlorides, oxychalcogenides, tellurites, molybdates, tungstates, chromates, phosphates, arsenates, vanadates, niobates, silicates, germanates, and borates. An overview of flux crystal growth is presented and specific crystal growth approaches are described with an emphasis on how and why they - versus some other method - are used and how they enable the preparation of specific classes of new materials.