From Ag2Sb2O6 to Cd2Sb2O7: Investigations on an anion-deficient to ideal pyrochlore solid solution

Laurita, Geneva; Vielma, Jason; Winter, Florian; Berthelot, Romain; Largeteau, Alain; Pöttgen, Rainer; Schneider, G.; Subramanian, M. A.

doi:10.1016/j.jssc.2013.11.007

Cited by 8 publications

(4 citation statements)

References 37 publications

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“…These diffraction peaks are indexed to a face-centered cubic lattice with Fd3m space group. 24 Considering ICP-AES revealed the presence of Tm in the samples, and in accordance with JCPDS 23-0590, the peaks cited above are assigned to a pyrochlore oxide, Tm 2 Ti 2 O 7 . 22 These peaks are marked as p in Fig.…”

Section: Xrdsupporting

confidence: 76%

Thermo-selective Tm_xTi_1−xO_2−x/2nanoparticles: from Tm-doped anatase TiO₂to a rutile/pyrochlore Tm₂Ti₂O₇mixture. An experimental and theoretical study with a photocatalytic application

et al. 2014

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This is an experimental and theoretical study of thulium doped TiO2 nanoparticles. From an experimental perspective, a method was used to synthesize thulium-doped TiO2 nanoparticles in which Tm(3+) replaces Ti(4+) in the lattice, which to our knowledge has neither been reported nor studied theoretically so far. Different proportions of anatase and rutile phases were obtained at different annealing temperatures, and XRD and Raman spectroscopy also revealed the presence of a pyrochlore phase (Tm2Ti2O7) at 1173 K. Thus, the structure of the Tm-doped nanoparticles was thermally-controlled. Furthermore, XPS showed the presence of Tm(3+) in the samples synthesized, which produces oxygen vacancies to maintain the local neutrality in the lattice. The presence of Tm(3+) in the samples led to changes in the UV-Vis absorption spectra, so they showed photoluminescence properties and new states in the band gap, which produce a new lower energy electronic transition than the main TiO2 one. Periodic DFT calculations were performed to understand the experimentally produced structures. The production of oxygen vacancies was analysed and the changes generated in the structure were fully detailed. The DOS and PDOS analyses confirmed the experimental results obtained using UV-Vis spectroscopy, and showed that the new electronic states in the band gap are due to interactions of the f state of Tm and the p state of O. Likewise, the charge study and the ELF analysis indicate that when Tm is introduced into the TiO2 structure, the Ti-O bond around the oxygen vacancy is strengthened. Finally, an example of a photocatalytic application was developed to show the high efficiency of the samples due to the heterojunction in the interfaces of the phases in the samples, which improved the charge separation and the good charge carrier mobility due to the presence of the pyrochlore phase, as was also shown theoretically.

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Section: Xrdsupporting

confidence: 76%

Thermo-selective Tm_xTi_1−xO_2−x/2nanoparticles: from Tm-doped anatase TiO₂to a rutile/pyrochlore Tm₂Ti₂O₇mixture. An experimental and theoretical study with a photocatalytic application

et al. 2014

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“…Pyrochlores are a class of complex ternary oxides with general formula A 2 B 2 O 7 , wherein, commonly, A-site cations are trivalent rare earths and B-site cations are tetravalent transition metals, with other valence states also reported . Pyrochlores are derived from the basic fluorite (BO 2 ) structure and exhibit ordering on both the cation and anion sublattices. ,− Interestingly, they contain structural oxygen vacancies (to compensate the lower valence A 3+ cations), which are responsible for some of their unusual properties. , For bulk pyrochlores, a plethora of literature exists from both theoretical and experimental standpoints. − However, little is known about the actual structure and stability of their low-index surfaces. Recently, heterostructures of pyrochlores, involving interfaces with other materials, have also received attention. − Yet, the role of pyrochlore surface structure and composition at these interfaces is not clear.…”

Section: Introductionmentioning

confidence: 99%

Atomic-Scale Structure and Stability of the Low-Index Surfaces of Pyrochlore Oxides

2016

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The multifunctional properties of complex ternary oxides such as pyrochlores are often influenced by surface structure. Optimizing the surface-driven attributes of these materials necessitates a detailed understanding of the structure and chemical composition of those surfaces. Here we report atomistic simulations elucidating the diverse atomic-scale structures of a set of low-index surfaces [(100), ( 110), (111), and ( 112)] in pyrochlore compounds as a function of both A and B cation chemistry. In pyrochlores, the low-index facets are all dipolar, requiring the introduction of surface defects to eliminate the surface dipole. We find that, due to the corresponding higher coordination of the surface cations, the (110) facet is the most energetically stable in all of the compounds considered, an interesting contrast to fluorite, in which the (111) surface is most stable. We also reveal a correlation between the surface energy and the energy to disorder the pyrochlore as a function of B cation chemistry, implying a similar physical origin for the two phenomena. Further, we find that surface rumpling is common across all pyrochlore compounds. An even more interesting feature emerging at these surfaces is the formation of extended structural defects such as steps and trenches, which are found to be stable after high-temperature annealing. As the formation of these features is a consequence of surface defects introduced to eliminate the surface dipole, we propose that the superior surface properties of materials of pyrochlores are due to these extended structural features, which are a direct consequence of the inherent dipole at the surfaces.

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“…The large A ions occupy distorted cubic sites, the B site has octahedral coordination, and the anions sit in 7/8 of the tetrahedral sites, the X site corresponds to the 48f Wycoff site and the X' site to the 8b site. 6 It is also often described as a rigid BX 6 octahedral network interpenetrated with a more flexible network of A 2 X' chains. Pyrochlore oxides are known to exhibit diverse functionalities, including oxide ion conduction as electrolytes or mixed conductors, 7,8 enabled by the intrinsic anion vacancies and ease of migration through unoccupied octahedral sites.…”

Section: Introductionmentioning

confidence: 99%

“…The pyrochlore structure A 2 B 2 X 6 X' can be thought of as a defective fluorite (space group Fd3̅ m) with ordered cation and anion vacancies. The large A ions occupy distorted cubic sites, the B site has octahedral coordination, and the anions sit in 7/8 of the tetrahedral sites, the X site corresponds to the 48f Wycoff site and the X' site to the 8b site 6 . It is also often described as a rigid BX 6 octahedral network interpenetrated with a more flexible network of A 2 X' chains.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and characterization of a pyrochlore solid solution in the Na₂O‐Bi₂O₃‐TiO₂ system

2020

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The compositional limits of a previously reported (J. Am. Ceram. Soc., 61, 5-8. (1978)) but relatively unstudied sodium-bismuth titanate pyrochlore solid solution are revised and their electrical properties presented. The pyrochlore solid solution we report forms via a different mechanism to that originally reported and occurs in a different location within the Na 2 O-Bi 2 O 3-TiO 2 ternary system. In both cases, relatively large amounts of vacancies are required on the A-sites and on the oxygen sites, similar to that reported for undoped 'Bi 2 Ti 2 O 7 ' pyrochlore. In contrast to 'Bi 2 Ti 2 O 7 ', this ternary pyrochlore solid solution can be prepared and ceramics sintered using conventional solid-state methods; however, the processing requires several challenges to be overcome to obtain dense ceramics. This cubic pyrochlore series has low electrical conductivity (and does not exhibit any evidence of oxideion conduction) and exhibits relaxor ferroelectric behavior with a broad permittivity maximum of ~100 near room temperature. Variable temperature neutron diffraction data do not provide any conclusive evidence for a phase transition in the pyrochlore solid solution between ~4 and 873 K.

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From Ag2Sb2O6 to Cd2Sb2O7: Investigations on an anion-deficient to ideal pyrochlore solid solution

Cited by 8 publications

References 37 publications

Thermo-selective Tm_xTi_1−xO_2−x/2nanoparticles: from Tm-doped anatase TiO₂to a rutile/pyrochlore Tm₂Ti₂O₇mixture. An experimental and theoretical study with a photocatalytic application

Thermo-selective Tm_xTi_1−xO_2−x/2nanoparticles: from Tm-doped anatase TiO₂to a rutile/pyrochlore Tm₂Ti₂O₇mixture. An experimental and theoretical study with a photocatalytic application

Atomic-Scale Structure and Stability of the Low-Index Surfaces of Pyrochlore Oxides

Synthesis and characterization of a pyrochlore solid solution in the Na₂O‐Bi₂O₃‐TiO₂ system

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From Ag2Sb2O6 to Cd2Sb2O7: Investigations on an anion-deficient to ideal pyrochlore solid solution

Cited by 8 publications

References 37 publications

Thermo-selective TmxTi1−xO2−x/2nanoparticles: from Tm-doped anatase TiO2to a rutile/pyrochlore Tm2Ti2O7mixture. An experimental and theoretical study with a photocatalytic application

Thermo-selective TmxTi1−xO2−x/2nanoparticles: from Tm-doped anatase TiO2to a rutile/pyrochlore Tm2Ti2O7mixture. An experimental and theoretical study with a photocatalytic application

Atomic-Scale Structure and Stability of the Low-Index Surfaces of Pyrochlore Oxides

Synthesis and characterization of a pyrochlore solid solution in the Na2O‐Bi2O3‐TiO2 system

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Thermo-selective Tm_xTi_1−xO_2−x/2nanoparticles: from Tm-doped anatase TiO₂to a rutile/pyrochlore Tm₂Ti₂O₇mixture. An experimental and theoretical study with a photocatalytic application

Thermo-selective Tm_xTi_1−xO_2−x/2nanoparticles: from Tm-doped anatase TiO₂to a rutile/pyrochlore Tm₂Ti₂O₇mixture. An experimental and theoretical study with a photocatalytic application

Synthesis and characterization of a pyrochlore solid solution in the Na₂O‐Bi₂O₃‐TiO₂ system