Crystalline ceramics are intensively investigated as effective materials in various nuclear energy applications, such as inert matrix and accident tolerant fuels and nuclear waste immobilization. This paper presents an analysis of the current status of work in this field of material sciences. We have considered inorganic materials characterized by different structures, including simple oxides with fluorite structure, complex oxides (pyrochlore, murataite, zirconolite, perovskite, hollandite, garnet, crichtonite, freudenbergite, and P-pollucite), simple silicates (zircon/thorite/coffinite, titanite (sphen), britholite), framework silicates (zeolite, pollucite, nepheline /leucite, sodalite, cancrinite, micas structures), phosphates (monazite, xenotime, apatite, kosnarite (NZP), langbeinite, thorium phosphate diphosphate, struvite, meta-ankoleite), and aluminates with a magnetoplumbite structure. These materials can contain in their composition various cations in different combinations and ratios: Li–Cs, Tl, Ag, Be–Ba, Pb, Mn, Co, Ni, Cu, Cd, B, Al, Fe, Ga, Sc, Cr, V, Sb, Nb, Ta, La, Ce, rare-earth elements (REEs), Si, Ti, Zr, Hf, Sn, Bi, Nb, Th, U, Np, Pu, Am and Cm. They can be prepared in the form of powders, including nano-powders, as well as in form of monolith (bulk) ceramics. To produce ceramics, cold pressing and sintering (frittage), hot pressing, hot isostatic pressing and spark plasma sintering (SPS) can be used. The SPS method is now considered as one of most promising in applications with actual radioactive substances, enabling a densification of up to 98–99.9% to be achieved in a few minutes. Characteristics of the structures obtained (e.g., syngony, unit cell parameters, drawings) are described based upon an analysis of 462 publications.

A systematic analysis of orthophosphates of framework (tetrahedral-octahedral) structure, belonging to langbeinite structural type (cubic cell, space group P2₁3), is performed. The langbeinite structure is considered as favorable for environmentally safe crystalline forms of radioactive waste solidification. Experimental data on the compositions of known phosphates of such structure, on isomorphism of cations in various crystallographic positions, and on specific features of distribution of various cations in them are summarized. Possible formula compositions of isostructural phosphates are calculated. Some of them have already been synthesized (data given in this paper), whereas other phosphates are yet unknown. The structural-chemical aspect was also applied to langbeinite-like phosphates of f elements, some of which were prepared in accordance with the “crystal-chemical prediction.” Phosphates of the rhombohedral [NaZr₂(PO₄)₃ type, NZP] and cubic (langbeinite type) tetrahedral-octahedral framework modifications, their cationic compositions, and structural features are compared. Properties of phosphates of langbeinite structure, useful in the development of new materials for radiochemical applications, and examples of possible use of crystal-chemical principles in solution of these problems are discussed.