Geodesic
Pyrochlore phase in the Bi$_2$O$_3$–Fe$_2$O$_3$–WO$_3$–(H$_2$O) system: its stability field in the low-temperature region of the phase diagram and thermal stability
Nanosistemy: fizika, himiâ, matematika, Tome 15 (2024) no. 2, pp. 240-254 Cet article a éte moissonné depuis la source Math-Net.Ru

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The concentration stability field localization of the pyrochlore-structured compounds of variable composition formed in the Bi$_2$O$_3$–Fe$_2$O$_3$–WO$_3$ system under hydrothermal conditions at a temperature of $T$ = 200$^\circ$C and a pressure of $P$ = 7 MPa was determined. It was found that the pyrochlore-structured compounds stability field is longitudinally limited within the atomic ratios 0.47 $$ Bi/W $$ 1.25, and in the transverse direction within 1.14 $$ Bi/Fe $$ 1.87. It was shown that the pyrochlore phase cubic unit cell parameter a depends on the compound chemical composition as follows: it increases linearly from $\sim$ 10.3319 $\mathring{\mathrm{A}}$ to $\sim$ 10.4199 $\mathring{\mathrm{A}}$ with an increase in the Bi/W atomic ratio from $\sim$ 0.47 to $\sim$ 1.25. It was established that from the Bi$_2$O$_3$–WO$_3$ system side, there is a region of two-phase equilibrium, in which a pyrochlore phase of variable composition coexists with the Bi$_2$WO$_6$ compound, which is formed in the form of plate-like (thickness $h\sim$ 50–100 nm) nanoparticles. It was shown that from the Bi$_2$O$_3$–Fe$_2$O$_3$ system side, there is a region of compositions, in which the pyrochlore phase of the most enriched in bismuth oxide composition coexists with the Bi$_2$WO$_6$ compound, which is formed in the form of rod-shaped ($h\sim$ 10–30 nm) nanoparticles, and with the X-ray amorphous phase composition, formed in the form of nanocrystalline particles about 10 nm in size. It was found that the higher temperature point of the pyrochlore-structured compounds stability field does not exceed 725$^\circ$C, which allows them to be synthesized only by “soft chemistry” methods.
Keywords: pyrochlore-structured phase, hydrothermal synthesis, crystal structure, phase diagram, thermal stability. 
@article{NANO_2024_15_2_a10,
     author = {Makariy S. Lomakin and Olga V. Proskurina and Aleksandr A. Levin and Vladimir N. Nevedomskiy},
     title = {Pyrochlore phase in the {Bi}$_2${O}$_3${{\textendash}Fe}$_2${O}$_3${{\textendash}WO}$_3${{\textendash}(H}$_2${O)} system: its stability field in the low-temperature region of the phase diagram and thermal stability},
     journal = {Nanosistemy: fizika, himi\^a, matematika},
     pages = {240--254},
     year = {2024},
     volume = {15},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/NANO_2024_15_2_a10/}
}
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%A Vladimir N. Nevedomskiy
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Makariy S. Lomakin; Olga V. Proskurina; Aleksandr A. Levin; Vladimir N. Nevedomskiy. Pyrochlore phase in the Bi$_2$O$_3$–Fe$_2$O$_3$–WO$_3$–(H$_2$O) system: its stability field in the low-temperature region of the phase diagram and thermal stability. Nanosistemy: fizika, himiâ, matematika, Tome 15 (2024) no. 2, pp. 240-254. http://geodesic.mathdoc.fr/item/NANO_2024_15_2_a10/