[en] Tetrahedron-octahedral (Td-Oh) framework orthophosphates were studied with a view to developing phosphate ceramics for radiochemical and other applications. Framework phosphates containing trivalent elements can be presented by the following compositions: [T^III_3/2T^V_1/2(PO₄)₃]⁰ → [T^IIIT^V(PO₄)₃]^-1 → [T^III_1/2T^V_3/2(PO₄)₃]^-2 and [T^IIIT^IV(PO₄)₃]^-2 → [T^IIIT^III(PO₄)₃]^-3 → [T^IIIT^II(PO₄)₃]^-4, where T^II, T^III, T^IV, T^V are elements in the oxidation states +2, +3, +4, +5, respectively. The subjects of research were: K₂T^IIIZr(PO₄)₃, where T^III are Y and lanthanides from Pr to Lu; K₂T^III_3/2Ta_1/2(PO₄)₃, where T^III = Y, Gd-Yb; T^I₂T^IIIZr(PO₄)₃, where T^I = Rb, Cs; T^III = Pr, Er; KBaT^III₂(PO₄)₃, where T^III = Yb, Er; CsBaT^III₂(PO₄)₃, where T^III = Dy-Yb; T^IBaFe_2-xPr_x(PO₄)₃, where T^I = K, Cs, x = 0,25; 0,5; 0,75. Synthesis of the samples was performed by two different methods: by solid state reaction for Ta-containing compounds and by the sol-gel method for the remaining compounds. The substances were investigated by X-ray powder diffraction, IR spectroscopy, powder neutron diffraction. The compounds crystallized in the cubic structural modification as existing in langbeinite. Empiric rules for constructing new phosphates compositions containing f-elements and possessing the langbeinite structure were found. The limits of lanthanide incorporation into the [T₂(PO₄)₃]^n- framework (n = 0, 1, 2, 3, 4) were examined. The effect of size on the number of the lanthanide-occupied framework sites was found. The regions of thermal stability, thermal expansion and hydrothermal behaviour of the new substances were determined. The composition of the phosphates, their structural characteristics and stability parameters were investigated in view of a the crystallochemical concept of developing prospective materials for the solidification of high level radioactive wastes and other applications

[en] Ln₃PO₇(Ln-La-Er) oxyphosphates are obtained through solid phase synthesis method. La₃PO₇ monocrystals are grown. Structural changes in the La-Er oxyphosphates series are evaluated through roentgenography and IR-spectroscopy methods; referral of the IR- and RR-spectra to iscillations of interatomic bonds Ln-O, P-O, O-P-O is made; isostructure, sp.gr.Cm. is established and crystal cell parameters for the whole series of compounds is determined. 16 refs.; 3 figs.; 3 tabs

[en] A series of double phosphates of formula AM₂(PO₄)₃, where A = Li, Na, K, Rb, Cs; M = U, Np, Pu, is prepared by solid-state reactions. Various polymorphic modifications of AM₂(PO₄)₃ are identified by using X-ray diffraction and IR spectroscopic analyses of the products from stepwise annealing. The crystal structure type, thermal stability of the modifications, and nature of the polymorphic transformations depend on the nature of the actinide and alkali metal

[en] The synthesis and results of the X-ray diffraction examination of complex orthophosphates involving the cations Ca²⁺, Cd²⁺, Gd³⁺, Ti⁴⁺, Hf⁴⁺, Ce⁴⁺, U⁴⁺, and Pu⁴⁺ are described. Crystalline products containing either cerium or plutonium or these two elements together were prepared. Cerium was used as plutonium simulator. Phosphates containing cations Ti⁴⁺ and Hf⁴⁺ were found to form two-phase products. One of these phases was assumed to be of the NaZr₂(PO₄)₃ (NZP) type, the other one of the CePO₄ type (monazite). Formation of single-phase products with a monazite structure was found in the specimens that did not contain Ti and Hf. X-ray diffraction characteristics of synthesised phases were identified. An effect of the cation composition on the phase formation and also the effect of the cation size on the crystal lattice parameters of the formed phases were established. (author)

[en] The conditioning of radioactive waste from nuclear power plants and in some countries even of weapons plutonium is an important issue for science and society. Therefore the research on appropriate matrices for the immobilization of fission products and actinides is of great interest. Beyond the widely used borosilicate glasses, ceramics are promising materials for the conditioning of actinides like U, Np, Pu, Am, and Cm. Monazite-type ceramics with general composition LnPO₄ (Ln = La to Gd) and solid solutions of monazite with cheralite or huttonite represent important materials in this field. Monazite appears to be a promising candidate material, especially because of its outstanding properties regarding radiation resistance and chemical durability. This article summarizes the most recent results concerning the characterization of monazite and respective solid solutions and the study of their chemical, thermal, physical and structural properties. The aim is to demonstrate the suitability of monazite as a secure and reliable waste form for actinides. (orig.)

[en] This article examines the possibility of the existence of ternary phosphates of the rare earth elements (REE) containing two large alkali cations in order to establish the morphological and physicochemical characteristics in the entire group of ternary REE phosphates. The synthesis of the ternary rubidium-cesium-REE phosphates was carried out with molten charges that did not contain an excess of components. Analysis for the uncommon alkali cations was done by the atomic absorption technique; for holmium, by complexometric titration; and for phosphorus, by gravimetry as NH₄CdPO₄. The data obtained fully confirm the composition of Rb₂CsLn(PO₄)₂

No abstract available

[en] Raman spectra of anhydrous crystalline samples of all of the lanthanide orthophosphates (with the exception of PmPO₄) have been obtained. These data were interpreted in a systematic manner based on the known structures of these compounds. Assignments and correlations have been made for many of the observed bands. (author)

[en] Amorphous LaPO₄, EuPO₄, GdPO₄, ScPO₄, and fluorapatite [Ca₅(PO₄)₃F] were irradiated by electron beam in a TEM. Irradiations were done at -150 to 300 C, 80 to 200 keV, and current densities from 0.3 to 16 A/cm². In all cases, the materials crystallized to form a randomly oriented polycrystalline assemblage. Crystallization is driven dominantly by inelastic processes, although ballistic collisions with target nuclei can be important above 175 keV, particularly in apatite. Using a high current density, crystallization is so fast that continuous lines of crystallites can be ''drawn'' on the amorphous matrix

No abstract available