New insight into the crystal chemistry of uranium and thorium borates, borophosphates and borate-phosphates

This dissertation work is devoted to a systematic study of phase formation, their structures and properties in the AI/AII-U/Th-B-(P)-O system at different conditions. This workresulted in obtaining and characterizing around thirty novel uranium and thorium phases. Among them, several compounds uncovered novel structural topologies and differentphysicochemical properties. As an example, a lead uranyl borate (LUBO) is the first zeolitelikepolyborate material observed in the uranyl oxo-borates system. It possesses a uniqueboron-oxygen open framework structure with multi-intersection channels. This robustpolyborate framework demonstrates high thermal stability up to 690 °C.An introduction of [PO4]3- ortho-phosphates anions into the above mentioned oxo-boratesystem leads to the formation of complex novel uranium borophosphates, borate-phosphatesand phosphates. Among them, three novel highly porous uranyl borophosphates with uniquethree dimensional open framework structures have been structurally characterized. One ofthese phases, namely, Cs3(UO2)3[B(PO4)4]∙(H2O)0.5 has been proven to be a promising ionicexchanger. In the Th-B-O system, a new polymorphic modification of ThB2O5 has been isolated atambient pressure. A further investigation of the ThB2O5 phase diagram demonstrates veryunusual stability ranges of both polymorphic modifications. It has been shown that the natureof the flux plays a crucial role in the formation of both polymorphic modifications. The structures of all materials obtained in above mentioned systems have been determined by single crystal X-ray diffraction (SXRD) with a further characterization bypowder X-ray diffraction (PXRD), Infrared (IR)/Raman spectroscopy, thermogravimetricanalysis (TGA), differential scanning calorimetry (DSC), and energy dispersive X-rayspectroscopy (EDS). The computational studies of the phase formation in Th-B-O systemhave been performed using density functional theory (DFT).The results of the performed study clearly demonstrate that the counter cations play akey role in the structural formation of phases in studied systems. Consequently, the structures of compounds determine their physicochemical properties