Victoria S. Kurazhkovskaya

Double Phosphates of Ce(IV) and Some Mono- and Divalent Elements: Synthesis and Crystal Structure

A series of new double orthophosphates of cerium and mono- and divalent elements ACe2(PO4)3, B0.5Ce2(PO4)3, and B1.5Ce1.5(PO4)3 (A = Li, Na, K, Rb, and Cs; B = Mg, Ca, Sr, Ba, and Cd) were synthesized and characterized by X-ray diffraction and IR spectroscopy. The thermal behavior of the phosphates was studied. General crystallochemical features of phase formation in the series of stoichiometric ortho-phosphates of 4f and 5f elements are discussed.

Synthesis and structure of CsLi0.5Al0.5PO4

A new phosphate CsLi0.5Al0.5PO4 with a structure related to the β-tridymite structure has been synthesized by a precipitation method. X-ray powder diffraction, electron probe microanalysis, second harmonic generation of laser radiation, and IR spectroscopy have been used for studying the compound. Differential scanning calorimetry shows that the synthesized phosphate undergoes phase transitions at Ttr = 68 and 130°C. The crystal structure of CsLi0.5Al0.5PO4 was refined on the basis of X-ray powder diffraction data by the Rietveld method in space group P21/a (Z = 8) with the unit cell parameters a = 17.8323(3) Å, b = 5.4250(1) Å, c = 9.3666(2) Å, β = 89.984(8)°, V = 906.10(9) Å3.

Relationship between IR spectra and crystal structures of β-tridymite-like CsM2+PO4 compounds

Caesium-bearing phosphates with the β -tridymite structure are considered as storage container for radioactive Cs. In this context, double phosphates of caesium and divalent cations, CsM 2+ PO 4 where M 2+ = Zn, Co, Mn, Mg, and Ni, have been synthesised by the precipitation method as powders and investigated by infrared spectroscopy in combination with factor-group analyses for band assignment. Comparison of the IR pattern of CsZnPO 4 and CsCoPO 4 confirms that they are isomorphic (space group P 1 2 1 / a 1 at room conditions). Both undergo T -induced phase transitions: one at 260 °C ( Pn 2 1 a) and another one at 310 °C ( Pnma ). High-temperature IR spectra of the orthorhombic modifications of CsZnPO 4 are presented and assigned. Comparison of the IR-spectrum of CsMnPO 4 with that of CsZnPO 4 ( Pn 2 1 a ) confirms that it crystallizes in the orthorhombic structure at room conditions ( Pn 2 1 a) . CsMgPO 4 crystallizes at room conditions in the orthorhombic space group Pnma , however, it tends to hydrate immediately after quenching in air forming the cubic hydrate CsMgPO 4 ·6H 2 O (space group F 43 m ). The liability to hydration is also characteristic for CsNiPO 4 . Temperature-dependent IR spectroscopy, X-ray diffraction, thermal analyses (TGA, DTA) and second-harmonic generation (SHG) revealed that pure anhydrous CsMgPO 4 (space group Pnma ) can only be stored in air at temperatures higher than 150 °C. Our study proves that CsM 2+ PO 4 , where M 2+ = Zn, Co, Mn, may be stable containers for radioactive Cs at room temperatures. However, CsMgPO 4 and CsNiPO 4 can only be used as crystalline matrices for the immobilisation of radioactive Cs when stored at temperature higher than 150 °C due to their hydrolytic instability in air. The difference in the structures of CsMg phosphate and Cs phosphates with Zn, Co, and Mn is caused by the different liability of these cations to form either ionic or covalent chemical bonds.

The synthesis and structure of alkaline earth and cerium (IV) phosphates (Ce, B, □)[PO4] (B = Mg, Ca)

Double orthophosphates (Ce(IV), B, □)[PO4] (B = Mg, Ca) were obtained after thermal treatment of gels with stoichiometric contents of components. The compounds obtained were characterized by X-ray diffraction analysis, infrared spectroscopy, and the electron spin resonance technique. The crystal structures were refined by the Rietveld method within the sp. gr. P21/n. The refinement was performed in the anisotropic approximation of atomic displacements for cations and isotropic approximation for oxygen.

Synthesis and Thermal Expansion of Complex Niobium(V) Phosphates with Bivalent Elements

Thermal expansion of niobium phosphates, new representatives of the family of structural analogs of [NaZr2(PO4)3], was studied. These compounds possess high thermomechanical stability because of the unique ability of their structure to expand-contract along different crystallographic directions under thermal treatment.

Investigation of Systems (A, A′) 2 O-TiO 2 -P 2 O 5 with Mutually Different Alkali Elements

The interest in the NaZr2(PO4)3 (NZP) structural family arises due to its potential use as host for radioactive wastes. In comparison with other waste forms the advantages of the NZP ceramics lie in its ability to accommodate a large number of multivalent ions into a single crystalline phase and chemical bonding of alkali elements. Introduction in a host phase of cheaper and lighter titanium instead of the commonly used zirconium permits us to obtain cheaper ceramic with larger content of alkali elements. Single phase phosphates corresponding to crystalline solution (continuous or limited) with the structure similar to NZP were found in the series of compounds with the general formula A1−x+ 4nA′xTi2−n(PO4)3, with n= 0, 0.5 and 1, and 0≤ x≤ 1+ 4n containing Li-Na, Li-K, Li-Rb, Li-Cs, Na-K, Na-Cs, K-Rb, K-Cs, Rb-Cs in pairs. The phosphates were prepared by direct solid state reactions in air and studied by powder x-ray diffraction, infrared absorption spectroscopy, and electron microprobe analyses. Leach studies were performed at 25◦C for 3 weeks in deionized water.