NEXAFS and XPS spectra of Ьn doped bismuth magnesium tantalate pyrochlores

Nadezhda A. Zhuk ; Sergey V. Nekipelov ; Alexandra V. Koroleva ; Alexey M. Lebedev ; Dmitriy S. Beznosikov

Žurnal Sibirskogo federalʹnogo universiteta. Matematika i fizika, Tome 17 (2024) no. 4, pp. 544-553

Résumé

According to X-ray powder phase analysis, Bi$_2$Mg$_x$Mn$_{1-x}$Ta$_2$O$_{9.5-\Delta}$ (x=0.3;0.5;0.7) samples synthesized using ceramic technology contain the main phase of cubic pyrochlore (space group Fd-3m) and the impurity phase BiTaO$_4$ of the triclinic modification (sp. Gr. P-1), the content of which is proportional to the degree of doping with manganese. The unit cell parameter of the pyrochlore phase increases uniformly with increasing index x(Mg) from 10.4970(8) at x=0.3 to 10.5248(8) Å (x=0.7), obeying the Vegard rule. The electronic state of all ions included in Bi$_2$Mg$_x$Mn$_{1-x}$Ta$_2$O$_{9.5-\Delta}$ was studied using X-ray spectroscopy. According to NEXAFS and XPS data, it was established that doping with magnesium does not change the oxidation state of bismuth and tantalum in pyrochlore. Meanwhile, in the Ta4f$_-$, Bi4f$_{7/2}$ and Bi4$_{f5/2}$ spectra of the samples, an energy shift of the absorption bands towards lower energies is observed, which is typical for bismuth and tantalum ions with an effective charge of (+3-$\delta$) and (+5-$\delta$), caused by the distribution of manganese(II) and magnesium(II) ions in the position of bismuth and tantalum. According to NEXAFS and XPS spectroscopy, manganese ions in the samples have oxidation states predominantly +2 and +3, the proportion of which increases with increasing manganese content in the samples.

Détail

Keywords: pyrochlore, Zn,Mg doping, XPS and NEXAFS spectroscopy.
Mots-clés : BiTaO$_4$