Electrical conductivity anomaly around fluorite–pyrochlore phase boundary

Yamamura, Hiroshi; Nishino, Hanako; Kakinuma, Katsuyoshi; Nomura, Katsuhiro

doi:10.1016/s0167-2738(02)00874-3

Cited by 223 publications

(122 citation statements)

References 16 publications

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“…The dual Yb+Gd intermix doping causes a distinctly enhanced total conductivity as compared to unmodified Nd 2 Zr 2 O 7 and singly Gd-doped zirconate ceramics at identical temperature levels. Yamamura et al reported that the total conductivity increased as the average of the ionic radii of A-site rare-earth cations decreased from 0.1160 to 0.1066 nm in the A 2 Zr 2 O 7 system [24], which is consistent with the results in this work. Clearly, the total conductivity of each composition gradually increases with increasing temperature from 673 to 1,173 K. From Figure 5, the total conductivity of its doped zirconate ceramics increases in the order of r(Nd 2 Zr 2 O 7 ) < r(Nd 1.8 ceramics is almost independent of oxygen partial pressure from 1.0 × 10 -4 to 1.0 atm at all test temperature levels, respectively, which indicates that the conduction is purely ionic conductivity with negligible electronic conduction [25].…”

Section: Resultssupporting

confidence: 92%

Improvement of Electrical Conductivity of Trivalent Rare‐earth Cation‐doped Neodymium Zirconate by Co‐doping Gadolinium and Ytterbium

2010

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Pyrochlore oxides of A2Zr2O7, where A represents trivalent rare‐earth elements, have a high electrical conductivity, which makes them suitable for applications as high‐temperature solid electrolytes. The influence of Gd and Yb cations co‐doping at the Nd site on structure and electrical conductivity of a pyrochlore oxide Nd2Zr2O7 is investigated using X‐ray diffraction and impedance spectra measurements. Different zirconate ceramics of Nd2Zr2O7, Nd1.8Gd0.2Zr2O7, Nd1.8Gd0.1Yb0.1Zr2O7, Nd1.4Gd0.6Zr2O7 and Nd1.4Gd0.3Yb0.3Zr2O7 are prepared by pressureless‐sintering method at 1,973 K for 10 h in air. Nd2Zr2O7 doped with Gd and Yb cations at the Nd site exhibit a single phase of pyrochlore‐type structure. The measured values of the total conductivity obey the Arrhenius relation. Nd2Zr2O7 and its doped zirconate ceramics are oxide‐ion conductors in the oxygen partial pressure range of 1.0 × 10–4 to 1.0 atm at all test temperature levels. The total conductivity increases with reducing average ionic radii of A‐site rare‐earth cations. The dual Yb+Gd intermix doping causes a distinctly enhanced total conductivity as compared to unmodified Nd2Zr2O7 and singly Gd‐doped zirconate ceramics. The highest total conductivity value obtained in this work is 1.02 × 10–2 S cm × 1 at 1,173 K for Nd1.4Gd0.3Yb0.3Zr2O7 ceramic.

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Section: Resultssupporting

confidence: 92%

Improvement of Electrical Conductivity of Trivalent Rare‐earth Cation‐doped Neodymium Zirconate by Co‐doping Gadolinium and Ytterbium

2010

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“…In a spin-ice, each tetrahedron has two spins pointing inwards and two outwards (so-called ice rules [1,3]). Other unusual behaviors have also been observed in A 2 B 2 O 7 pyrochlores, including spin-glass [4][5][6], and spin-liquid [4] states, as well as magnetic configurations modified by quantum fluctuations [1,[7][8][9][10]. The qualities of any given A 2 B 2 O 7 compound are principally dictated by the elements A and B, but can be strongly altered by structural defects, particularly stuffing of magnetic A 3+ ions onto nonmagnetic B 4+ sites and oxygen, A or B site vacancies [1,[7][8][9][10].…”

Section: Introductionmentioning

confidence: 84%

Atomic structure study of the pyrochloreYb2Ti2O7and its relationship with low-temperature magnetic order

et al. 2017

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There has been great interest in the magnetic behavior of pyrochlore oxides with the general formula A 2 B 2 O 7 , in which rare-earth (A) and transition metal (B) cations are ordered on separate interpenetrating lattices of corner-sharing tetrahedra. Such materials exhibit behaviors including quantum spin-ice, (quantum) spin-liquid, and ordered magnetic ground states. Yb 2 Ti 2 O 7 lies on the boundary between a number of competing magnetic ground states. Features in the low-temperature specific heat capacity that vary in sharpness and temperature from sample to sample suggest that, in some cases, the magnetic moments order, while in others, the moments remain dynamic down to temperatures as low as ∼16 mK. In this paper, three different Yb 2 Ti 2 O 7 samples, all grown by the optical floating zone technique but exhibiting quite different heat capacity behavior, are studied by aberration-corrected scanning transmission microscopy (STEM). Atomic-scale energy-dispersive x-ray analysis shows that a crystal with no specific heat anomaly has substitution of Yb atoms on Ti sites (stuffing). We show that the detailed intensity distribution around the visible atomic columns in annular dark field STEM images is sensitive to the presence of nearby atoms of low atomic number (in this case oxygen) and find significant differences between the samples that correlate both with their magnetic behavior and measurements of Ti oxidation state using electron energy loss spectroscopy. These measurements support the view that the magnetic ground state of Yb 2 Ti 2 O 7 is extremely sensitive to disorder.

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“…[12][13][14][15]. Figure 3 shows the relationship between the lattice parameter of A 2 Zr 2 O 7 and the ionic radius of A reported by Shannon [16].…”

Section: Measurementsmentioning

confidence: 98%

Thermophysical Properties of Rare-Earth-Stabilized Zirconia and Zirconate Pyrochlores as Surrogates for Actinide-Doped Zirconia

et al. 2007

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Thermophysical properties of rare-earth-stabilized zirconia and zirconate pyrochlores, A 2 Zr 2 O 7 (A = La, Nd, Sm, Gd, Dy, Y), were evaluated by X-ray diffractometry, Raman spectroscopy, and the ultrasound pulse-echo method. Crystallographic analyses elucidated that had the pyrochlore structure, whereas Dy 2 Zr 2 O 7 and Y 2 Zr 2 O 7 had the defect fluorite structure. For lanthanide pyrochlores, the thermal expansion became smaller with increasing ionic radius of A and increasing crystal binding energy. The elastic moduli and Debye temperature evaluated using longitudinal and transverse sound velocities also depend on the ionic radius and binding energy, and hence these values related to mechanical properties increase with the ionic radius of A. On the other hand, Poisson's ratio was almost comparable among these pyrochlores. In addition, thermophysical properties of actinide pyrochlore are discussed in this study.

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Electrical conductivity anomaly around fluorite–pyrochlore phase boundary

Cited by 223 publications

References 16 publications

Improvement of Electrical Conductivity of Trivalent Rare‐earth Cation‐doped Neodymium Zirconate by Co‐doping Gadolinium and Ytterbium

Improvement of Electrical Conductivity of Trivalent Rare‐earth Cation‐doped Neodymium Zirconate by Co‐doping Gadolinium and Ytterbium

Atomic structure study of the pyrochloreYb2Ti2O7and its relationship with low-temperature magnetic order

Thermophysical Properties of Rare-Earth-Stabilized Zirconia and Zirconate Pyrochlores as Surrogates for Actinide-Doped Zirconia

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