Some properties of zirconates and stannates with the pyrochlore structure

Chapman, Rachel; Meadowcroft, D. B.; Walkden, A J

doi:10.1088/0022-3727/3/3/309

Cited by 20 publications

(11 citation statements)

References 16 publications

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“…Pyrochlores, depending on their compositions, 31,33 can either be ionic or MIEC. Zirconates of Nd, Gd, and Y showed electrical conductivity independent of P (O 2 ) at different oxygen partial pressures 34,35 . In the present work, the electrical conductivity of (Gd 1− x Eu x ) 2 Zr 2 O 7 is reported in the oxygen partial pressure range, e.g., 1.0 × 10 −4 to 1.0 atm at temperatures of 673–873 K. Figure 9 shows the electrical conductivity of (Gd 0.4 Eu 0.6 ) 2 Zr 2 O 7 as a function of oxygen partial pressure P (O 2 ) at different temperatures.…”

Section: Resultsmentioning

confidence: 57%

Electrical Properties of Gadolinium–Europium Zirconate Ceramics

Xia

Ouyang

Liu

2010

Journal of the American Ceramic Society

127

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(Gd1−xEux)2Zr2O7 (0≤x≤1.0) ceramics are prepared via a solid‐state reaction process at 1973 K for 10 h in air. (Gd1−xEux)2Zr2O7 (0.2≤x≤1.0) ceramics exhibit an ordered pyrochlore‐type structure; however, Gd2Zr2O7 has a disordered defect fluorite‐type structure. Raman spectroscopy analysis indicates that the degree of structural ordering increases with the increase of Eu content. The electrical properties of (Gd1−xEux)2Zr2O7 ceramics are investigated using complex impedance spectroscopy over a frequency range of 0.1 Hz to 20 MHz from 623 to 923 K. Electrical conductivity obeys the Arrhenius equation. Both the activation energy and the preexponential factor for grain conductivity decrease with increasing europium content from Gd2Zr2O7 (x=0) to Eu2Zr2O7 (x=1.0). The measured electrical conductivity of (Gd1−xEux)2Zr2O7 ceramics increases with increasing Eu content and temperature. Electrical conductivity of the pyrochlore‐type materials is higher than that of the defect fluorite‐type material in (Gd1−xEux)2Zr2O7 solid solution systems. The electrical conductivity of (Gd0.4Eu0.6)2Zr2O7 is almost independent of oxygen partial pressure from 1.0 × 10−4 to 1.0 atm. The high ionic transference number of (Gd0.4Eu0.6)2Zr2O7 ceramic at different temperatures proves that conduction is purely ionic with negligible electronic contribution.

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Section: Resultsmentioning

confidence: 57%

Electrical Properties of Gadolinium–Europium Zirconate Ceramics

Xia

Ouyang

Liu

2010

Journal of the American Ceramic Society

127

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“…21 On the other hand, zirconates of Nd, Gd, and Y showed only ionic conductivity under varied oxygen partial pressures. 22,23 It was found that if there is a possibility of forming more than one valance state, the chance of electronic conduction arises. 24 Abrantes et al 20 showed that for Yb 2 Ti 2 O 7 pyrochlore above 700 C the electronic contribution to the total electrical conductivity increased only under highly reducing conditions.…”

Section: A Ionic Conductivitymentioning

confidence: 99%

Nanocrystalline Nd_2–_yGd_yZr₂O₇ pyrochlore: Facile synthesis and electrical characterization

et al. 2009

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Three solid solutions of pyrochlores in the series Nd 2-years Gd y Zr 2 O 7 (y = 0.8, 1.0, 1.2) were synthesized by the gel combustion method using citric acid as fuel. This results in a soft agglomerate powder as verified by dynamic light scattering. The single-phase nature of the products has been confirmed by x-ray diffraction. The increase in full width at half-maxima in the Raman spectra with an increase in Gd 3+ content indicates that disorder increases with Gd 3+ content. The morphology and particle size of the products were investigated by transmission electron microscopy. Scanning electron microscopy study reveals that the sintered pellets have a density higher than 92% of theoretical densities. The total ionic conductivity measurements in the temperature range 375-800 C show that with the increase of disorder (Gd 3+ content) in the system the activation energy of conduction increases from 0.98 to 1.06 eV and the preexponential factor, which is proportional to the number of mobile species, also follow the same trend of increase. The total conductivity measured in reducing atmosphere shows no change in electrical conductivity, which verifies a negligible contribution of electronic contribution in this system.

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“…Zirconate pyrochlores, with the chemical formula A 2 Zr 2 O 7 (where A is a rare earth element), have attracted considerable attention because of their potential use as solid oxide fuel cell electrode materials, fluorescence screens, thermal-barrier coatings, high-temperature heating elements, oxidation catalysts, and refractory ceramic materials for use in magnetohydrodynamic power generation [1][2][3][4][5][6][7][8]. Because they exhibit remarkable resistance to structural amorphization under ion-beam irradiation [6] and high chemical durability (release rates typically <10 À5 g m À2 d À1 based on zirconium) [9], as well as the fact that zirconium has a low neutron absorption cross-section [7], zirconate pyrochlores have also been proposed as inert matrix materials for actinide burning [7,9] and host matrices for high level radioactive waste, especially for long half-life actinides [10].…”

Section: Introductionmentioning

confidence: 99%

Ab initio molecular dynamics simulations of ion–solid interactions in zirconate pyrochlores

et al. 2015

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In this study, an ab initio molecular dynamics method is employed to study low energy recoil events in zirconate pyrochlores (A 2 Zr 2 O 7 , A = La, Nd and Sm). It shows that both cations and anions in Nd 2 Zr 2 O 7 and Sm 2 Zr 2 O 7 are generally more likely to be displaced than those in La 2 Zr 2 O 7 . The damage end states mainly consist of Frenkel pair defects, and the Frenkel pair formation energies in Nd 2 Zr 2 O 7 and Sm 2 Zr 2 O 7 are lower than those in La 2 Zr 2 O 7 . These results suggest that the order-disorder structural transition more easily occurs in Nd 2 Zr 2 O 7 and Sm 2 Zr 2 O 7 resulting in a defect-fluorite structure, which agrees well with experimental observations. Our calculations indicate that oxygen migration from 48f and 8b to 8a sites is dominant under low energy irradiation. A number of new defects, including four types of cation Frenkel pairs and six types of anion Frenkel pairs, are revealed by ab initio molecular dynamics simulations. The present results may help to advance the fundamental understanding of the irradiation response behavior of zirconate pyrochlores.

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Some properties of zirconates and stannates with the pyrochlore structure

Cited by 20 publications

References 16 publications

Electrical Properties of Gadolinium–Europium Zirconate Ceramics

Electrical Properties of Gadolinium–Europium Zirconate Ceramics

Nanocrystalline Nd_2–_yGd_yZr₂O₇ pyrochlore: Facile synthesis and electrical characterization

Ab initio molecular dynamics simulations of ion–solid interactions in zirconate pyrochlores

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Some properties of zirconates and stannates with the pyrochlore structure

Cited by 20 publications

References 16 publications

Electrical Properties of Gadolinium–Europium Zirconate Ceramics

Electrical Properties of Gadolinium–Europium Zirconate Ceramics

Nanocrystalline Nd2–yGdyZr2O7 pyrochlore: Facile synthesis and electrical characterization

Ab initio molecular dynamics simulations of ion–solid interactions in zirconate pyrochlores

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Nanocrystalline Nd_2–_yGd_yZr₂O₇ pyrochlore: Facile synthesis and electrical characterization