Structure and mutual transformations of anhydrous and hydrous CsMgPO4

A complex study of the synthetic CsMgPO₄ phosphate with a ??-tridymite structure type is performed. It is found that CsMgPO₄ is an unstable phase. At room temperature in air, it absorbs water and turns into the CsMgPO₄ · 6H₂O crystal hydrate. The transformation of cubic CsMgPO₄ · 6H₂O into orthorhombic CsMgPO₄ proceeds upon heating to 150°C by the pattern of the first-order phase transition with the dehydration of the specimen.     

Standard thermodynamic functions of CaNi0.5Zr1.5(PO4)3 crystalline phosphate in the range of T → 0 to 640 K

The temperature dependence of the heat capacity C _p ^○ = f(T) of CaNi_0.5Zr_1.5(PO₄)₃ crystalline phosphate is studied by precision adiabatic vacuum and differential scanning calorimetry over the temperature range of 7–640 K. Its standard thermodynamic functions C _p ^○ (T), H ^○(T)-H ^○(0), S ^○(T), and G ^○(T)-H ^○(0) for the region T → 0 to 640 K and the standard entropy of formation at T = 298.15 K are calculated from the obtained experimental data. Using data on the low-temperature (30–50 K) heat capacity, the D fractal dimension of phosphate is determined and conclusions about the character of the topology of its structure have been made. The final results are compared to data from thermodynamic investigations of the structurally related crystalline phosphates Zr₃(PO₄)₄, Ni_0.5Zr₂(PO₄)₃, and Ca_0.5Zr₂(PO₄)₃.     

The study of the crystalline phosphates of kosnarite type structure containing different alkali metals

The incorporation possibilities of different alkali elements into crystalline phosphates A_1−xA′_xHf₂(PO₄)₃ (A=Li, Na, K, Rb, Cs) were studied, the formation regions of kosnarite solid solutions were determined. Na_0.5K_0.5Hf₂(PO₄)₃ crystal structure was studied by powder X-ray diffraction, and the distribution of alkali metals in kosnarite structure was found out. The phosphate crystallizes in the space group R3?c, with a=8.7295(1) Å, c=23.2023(4) Å, V=1531.24(4) Å³, Z=6; R_wp=6.15, R_p=4.43. The concentration region knowledge of the kosnarite phase existence and peculiarities of their phase formation in the A_1−xA′_xM₂(PO₄)₃ (M=Ti, Zr, Hf) systems allow us to choose phosphate matrice compositions suitable for solidification of reprocessing wastes of spent U-Pu nuclear fuels.     

Phosphates having the NaZr2(PO4)3 structure and containing titanium (or zirconium) and elements in oxidation degree 2+ (calcium or zinc)

Complex phosphates Ca_{0.5 + x} Zn _x E_{2 ? x} (PO₄)₃ (E = Ti, Zr) having NaZr₂(PO₄)₃ (NZP) structure have been prepared and characterized by X-ray diffraction, electron probe microanalysis, IR spectroscopy, and differential thermal analysis (DTA). Their phase formation has been studied by X-ray powder diffraction and DTA. The concentration and temperature fields of existence of these NZP phases have been determined: substitution solid solutions exist in the range of compositions where 0 ≤ x ≤ 0.5. The Ca_0.7Zn_0.2Ti_1.8(PO₄)₃ crystal structure has been refined by the Rietveld method (space group \(R\bar 3\) , a = 8.3636(4) Å, c = 21.9831(8) Å, V = 1331.7(1) ų, Z = 6). The framework in the NZP structure is built of octahedra, which are populated by titanium and zinc atoms, and PO₄ tetrahedra. Calcium atoms occupy extraframework positions. Extensive solid solution formation due to the accommodation of cations(2+) in the interstices within the NZP framework (M) and in the framework-forming octahedra (M′) makes it possible to design a plurality of new M_{0.5 + x} M′ _x E_{2 ? x} (PO₄)₃ phosphates with tailored structures.     

Secondary ion yields produced by keV atomic and polyatomic ion impacts on a self-assembled monolayer surface

A suite of keV polyatomic or 'cluster' projectiles was used to bombard unoxidized and oxidized self-assembled monolayer surfaces. Negative secondary ion yields, collected at the limit of single ion impacts, were measured and compared for both molecular and fragment ions. In contrast to targets that are orders of magnitude thicker than the penetration range of the primary ions, secondary ion yields from polyatomic projectile impacts on self-assembled monolayers show little to no enhancement when compared with monatomic projectiles at the same velocity. This unusual trend is most likely due to the structural arrangement and bonding characteristics of the monolayer molecules with the Au(111). Copyright 1999 John Wiley & Sons, Ltd.