Isovalent substitution of the anionic sublattice of phases with general composition KSrВі2(PO4)3-х(VO4)x (х = 0÷3.0)

1Strutynska, NYu.
1Slobodyanik, MS
Ramanovska, KS
1Taras Shevchenko National University of Kyiv
Dopov. Nac. akad. nauk Ukr. 2020, 7:79-85
Section: Chemistry
Language: Ukrainian

The peculiarities of an influence of the isovalent substitution in the anionic sublattice of the langbeinite-related matrix KSrВі2(PO4)3 on the formation of phosphate-vanadates KSrВі2(PO4)3–х(VO4)x have been investigated for values x = 0.1, 0.25, 0.5, 0.75 and 3.0 using the solid state reaction method. It was found that the single phase langbeinite-related (cubic system, space group Р213) phosphate-vanadates have been obtained at the no significant substitution of phosphate by a vanadate group with the values х = 0.1, 0.25 and 0.5. Calculated lattice parameters for prepared KSrВі2(PO4)3–х(VO4)x (х = 0.1, 0.25 and 0.5) are in the range 9.93-10.1 Å. In the case of phases with values х = 0.75 and 3.0, the mixtures of phases have been prepared. The presence of VO4- and PO4-tetrahedra in the composition of new phases KSrВі2(PO4)3–х(VO4)x (х = 0.1, 0.25, and 0.5) was confirmed by the vibration modes in the their FTIR-spectra in the ranges 980-800 and 900-1150 сm–1, respectively. Based on results of thermal analysis, the prepared new langbeinite-related phosphate-vanadate KSrВі2(PO4)2.75(VO4)0.25 and KSrВі2(PO4)2.5(VO4)0.5 melt at a temperature above 1000 ºС and contain 0.7-1.3 wt % of sorbed water. It was shown that an increasing amount of vanadate in the langbeinite-type structure led to a decrease in the band gap from 3.0 eV for KSrВі2(PO4)2.9(VO4)0.1 to 2.8 еV for KSrВі2(PO4)2.75(VO4)0.25. Obtained samples have been characterized using the powder X-Ray diffraction method, thermogravimetry, differential thermal analysis, and FTIR- and electronic spectroscopies.

Keywords: complex phosphate, langbeinite, powder X-ray diffraction, thermal analysis

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