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. 2022 Oct 31;15(21):7668.
doi: 10.3390/ma15217668.

Effect of Fe-Doping on Thermal Expansion and Stability of Bismuth Magnesium Tantalate Pyrochlorere

Nadezhda A Zhuk  1 , Maria G Krzhizhanovskaya  2 , Sergey V Nekipelov  3 , Viktor N Sivkov  3 , Danil V Sivkov  3
Affiliations

Effect of Fe-Doping on Thermal Expansion and Stability of Bismuth Magnesium Tantalate Pyrochlorere

Nadezhda A Zhuk et al. Materials (Basel). .

Abstract

A continuous series of solid solutions (Bi1.5Mg0.75-xFexTa1.5O7±Δ (x = 0-0.75)) with the pyrochlore structure were synthesized with the solid-phase method. It was shown that iron, like magnesium, is concentrated in the structure in the octahedral position of tantalum. Doping with iron atoms led to an increase in the upper limit of the thermal stability interval of magnesium-containing pyrochlore from 1050 °C (x = 0) up to a temperature of 1140 °C (x = 1). The unit cell constant a and thermal expansion coefficient (TEC) increase uniformly slightly from 10.5018 Å up to 10.5761 Å and from 3.6 up to 9.3 × 10-6 °C-1 in the temperature range 30-1100 °C. The effect of iron(III) ions on the thermal stability and thermal expansion of solid solutions was revealed. It has been established that the thermal stability of iron-containing solid solutions correlates with the unit cell parameter, and the lower the parameter, the more stable the compound. The TEC value, on the contrary, is inversely proportional to the cell constant.

Keywords: FeMg codoping; bismuth tantalate pyrochlore; iron; thermal expansion; thermal stability.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Dependence of the unit cell parameter on the content of iron ions in Bi1.5Mg0.75−xFexTa1.5O7±Δ solid solutions.
Figure 2
Figure 2
SEM micrographs of Bi1.5Mg0.75−xFexTa1.5O7−Δ (x = 0.375) ceramics.
Figure 3
Figure 3
Experimental (blue circles), calculated (solid red line) and difference (grey line) XRD patterns of Bi1.5Mg0.375Fe0.375Ta1.5O7−Δ.
Figure 4
Figure 4
The projection of Bi1.5Mg0.75−xFexTa1.5O7±Δ (x = 0.375) pyrochlore crystal structure onto (110) crystallographic plane.
Figure 5
Figure 5
Temperature dependences of unit cell parameters of Bi1.5Mg0.75Ta1.5O7 (1), Bi1.5Mg0.375Fe0.375Ta1.5O7−Δ (2), Bi1.5Fe0.75Ta1.5O7+Δ (3) pyrochlores.
Figure 6
Figure 6
Similarity of the nature of the change in the lattice parameter of Bi1.5Fe0.75Ta1.5O7+Δ upon substitution of Fe↔Mg (a) and under the influence of temperature (b).
Figure 7
Figure 7
Temperature dependences of TECs of Bi1.5Mg0.75Ta1.5O7 (1), Bi1.5Mg0.375Fe0.375Ta1.5O7−Δ (2) and Bi1.5Fe0.75Ta1.5O7+Δ (3) pyrochlores.
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