Crystal structure, dielectric and thermal properties of cobalt doped bismuth tantalate pyrochlore

Жук, Н. А.; Krzhizhanovskaya, Maria G.; Секушин, Н. А.; Sivkov, Danil V.; Abdurakhmanov, I.E.

doi:10.1016/j.jmrt.2022.12.059

Cited by 8 publications

(12 citation statements)

References 32 publications

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“…c.n-6 = 0.745 Å ) and magnesium (II) (R(Mg(II))c.n-6 = 0.72 Å ), and because some of the cobalt ions are oxidized to the Co(III) state, which has a much smaller radius than Сo(II). As was shown earlier [17], the presence of bismuth orthotantalate impurities in the samples can be associated with the placement of Co(II) ions, not only in the octahedral sublattice of tantalum(V), but also in the bismuth(III) sublattice, which is due to the higher radius of Co(II) ions than Mg(II). Large cobalt(II) ions are mainly distributed into the octahedral sublattice of tantalum(V), creating oxygen vacancies and causing stress in the octahedral framework due to their low charge and large size.…”

Section: Resultssupporting

confidence: 58%

“…Fd-3m:2, a = 10.5526(2) Å, Z = 8 (No. 227) [24] and Bi 1.49 Co 0.8 Ta 1.6 O 7.0 (a = 10.54051(3) Å) [17] compositions.…”

Section: Resultsmentioning

confidence: 99%

“…This distribution requires vacancies in the bismuth sublattice. It can be assumed that vacancies are formed as a result of the formation of bismuth orthotantalate as an impurity phase [17,24]. Apparently, to relieve the stress of the octahedral framework, a certain fraction of cobalt(II) ions is distributed into the crystallographic positions of bismuth(III).…”

Section: Resultsmentioning

confidence: 99%

“…Bismuth-containing pyrochlores are promising for use in multilayer ceramic capacitors, resistors, resonators, microwave sensors and filters, electrocatalysts and photocatalysts, due to their excellent dielectric properties. Currently, complex oxides with a pyrochlore structure based on bismuth tantalate and niobate, doped with 3D ions, are being actively studied [15][16][17][18][19][20]. Cobalt-containing pyrochlores based on bismuth tantalate have not been studied enough.…”

Section: Introductionmentioning

confidence: 99%

“…Cobalt-containing pyrochlores based on bismuth tantalate have not been studied enough. There is one known work [17] which shows that pyrochlore of the composition Bi 1.49 Co 0.8 Ta 1.6 O 7.0 contains heterovalent cobalt ions Co(II) and Co(III). Similar cobalt pyrochlores based on bismuth niobate have been extensively researched over a wide range of concentrations for the Bi 2 O 3 -CoO-Nb 2 O 5 system [12].…”

Section: Introductionmentioning

confidence: 99%

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NEXAFS and XPS Studies of Co Doped Bismuth Magnesium Tantalate Pyrochlores

Zhuk,

Makeev,

Koroleva

et al. 2024

Chemistry

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Co doped bismuth magnesium tantalate with a pyrochlore structure (sp. gr. Fd-3m) was synthesized for the first time using the standard ceramic method. Single phase Bi2Mg1−xCoxTa2O9 samples were found to be formed when x < 0.7 in the X-ray phase analysis. However, with a higher cobalt content in the samples, the impurity phase β-BiTaO4 (sp. gr. P-1) is detected, and its amount is proportional to the degree of cobalt doping. The formation of solid solutions is evidenced by a uniform increase in the unit cell parameter of the Co,Mg co doped bismuth tantalate phase with an increase in the content of cobalt ions in the samples from 10.5412(8) (x = 0.3) to 10.5499(8) Å (x = 0.7). The samples exhibit a porous microstructure consisting of chaotically oriented and partially fused elongated grains measuring 1–2 μm. The dependence of the ceramic grain size on the n(Mg)/n(Co) ratio was not determined. X-ray spectroscopy (ear dge X-ray bsorption ine tructure (NEXAFS) and X-ray photoelectron spectroscopy (XPS)) was used to study the charge state of ions in Bi2Mg1−xCoxTa2O9. The NEXAFS and XPS data showed that doping with cobalt and magnesium did not change the bismuth and tantalum oxidation states in pyrochlore; in particular, the ions maintained their oxidation states of Bi(+3), Mg(+2) and Ta(+5). The energy position of the peaks of the Ta4f-, Ta5p-, Ta4d spectra had a characteristic shift towards lower energies compared to the binding energy in pentavalent tantalum oxide Ta2O5. A shift towards lower energies is characteristic of a decrease in the effective positive charge; in particular, for the Ta4f and Ta4d spectra we presented, this energy shift was ΔE = 0.65 eV, and in the region of the Ta4d edge—0.55 eV. This in turn allowed for us to assume that tantalum atoms have the same effective charge +(5-δ). The oxidation state of cobalt ions was predominantly 2+ and partially 3+, according to NEXAFS spectroscopy data.

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Section: Resultssupporting

confidence: 58%

“…Fd-3m:2, a = 10.5526(2) Å, Z = 8 (No. 227) [24] and Bi 1.49 Co 0.8 Ta 1.6 O 7.0 (a = 10.54051(3) Å) [17] compositions.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%