Evidence of local defects in the oxygen excess apatite La9.67(SiO4)6O2.5 from high resolution neutron powder diffraction

Guillot, Stéphanie; Beaudet-Savignat, Sophie; Lambert, S.; Vannier, Rose‐Noëlle; Roussel, Pascal; Porcher, Florence

doi:10.1016/j.jssc.2009.09.031

Cited by 45 publications

(38 citation statements)

References 44 publications

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“…A vanadium sample holder was used. Since a few structural data had already been reported on Mg doped compound [18,41,42] and we recently published the structure of La 9.67 ❒ 0.33 Si 6 O 26.5 [6], neutron diffraction data were collected on La 9 Ba 1 Si 6 O 26.5 , La 9.67 ❒ 0.33 Si 5.5 Ge 0.5 O 26.5 , and La 9.83 ❒ 0.17 Si 5.5 Al 0.5 O 26.5 powders only. Experiments at high temperatures, 700°C, 800°C and 900°C, corresponding to the operating temperatures of the SOFCs were also carried out on La 9 Ba 1 Si 6 O 26.5 .…”

Section: Methodsmentioning

confidence: 99%

“…Indeed, they are chemically stable and exhibit good ionic conduction properties [3][4][5]. With general formula La 10−x □ x (SiO 4 ) 6 O 2 + 3x/2 , they crystallised in the P6 3 /m space group [6] and their structure is built upon [SiO 4 ] tetrahedra spaced with La cations located in two sites: a 7-coordinated one, 4f, and a 9-coordinated one, 6h, and two extra oxide ions located in channels along the c-axis, bordered by the La(6h) cation. As calcium phosphate apatites, the structure of these lanthanum silicates is very flexible, and it can accept a wide range of partial substitutions on both the Si and La sites.…”

Section: Introductionmentioning

confidence: 99%

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Effect of the dopant nature on the conductivity of oxygen overstoichiometric oxyapatites with controlled microstructures

et al. 2011

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of the dopant nature on the conductivity of oxygen overstoichiometric oxyapatites with controlled microstructures

et al. 2011

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“…For the silicates it has been shown that oxygen excess in the range, 0 ≤ x ≤ 0.5 is possible, while higher oxygen content, 0 ≤ x ≤ 1.0 has been achieved for the germanates [13,18,20,21]. For the silicate series, the exact location of extrastoichiometric oxygen, x, has attracted some controversy, with reports of interstitial sites close to the SiO4 tetrahedra, while in other studies, mobile oxygen at the centre of the channels has been claimed [4,8,9,10,12,13,23,27,35,36]. For the germanates, the situation appears more clearcut, with computer modeling, neutron diffraction and Raman studies indicating occupancy by oxygen sites close to the GeO4 tetrahedra leading to the formation of five coordinate Ge [10, 20-22, 37, 40].…”

Section: Introductionmentioning

confidence: 99%

Apatite germanates doped with tungsten: synthesis, structure, and conductivity

et al. 2011

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High oxygen content apatite germanates, La 10 Ge 6-x W x O 27+x , have been prepared by doping on the Ge site with W. In addition to increasing the oxygen content, this doping strategy is shown to result in stabilisation of the hexagonal lattice, and yield high conductivities. Structural studies of La 10 Ge 5.5 W 0.5 O 27.5 show that the interstitial oxygen sites are associated to a different degree with the Ge/WO 4 tetrahedra, leading to five coordinate Ge/W and significant disorder for the oxygen sites associated with these units.Raman spectroscopy studies suggest that in the case of the WO 5 units, the interstitial oxygen is more tightly bonded and therefore not as mobile as in the case of the GeO 5 units, thus not contributing significantly to the conduction process.2

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“…Guillot et al investigated the crystal structure of La 9.67 -(SiO 4 ) 6 O 2.5 using primarily Rietveld analysis of NPD patterns collected at 3, 100, and 300 K. 87) They refined the structure parameters on the basis of the model with space group P6 3 /m. They compared R wp values for the models with and without the O5(12i) site, and the structure model with the O5(12i) site was concluded to be promising.…”

Section: Crystal Structure Model After the Discovery Of Oxygen-ion Comentioning

confidence: 99%

Research progress in nondoped lanthanoid silicate oxyapatites as new oxygen-ion conductors

Kobayashi

Sakka

2014

J. Ceram. Soc. Japan

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The discovery of oxygen-ion conductivity and changes in the crystal-structure model of nondoped lanthanum silicate oxyapatites are reviewed from the researches which led to the discovery to current work. The oxygen-ion conductivity of lanthanoid silicate oxyapatites was discovered by Nakayama et al., during development of new oxide lithium-ion conductors. Although samples with compositions of LiRESiO 4 (RE = La, Nd, Sm, Gd, Dy) were initially reported to be single phases with the same crystal structure, the accurate crystal structure of LiRESiO 4 was not clarified until later. The crystal structure determined from X-ray diffraction patterns of LiLnSiO 4 was revised as oxyapatite by another group. The chemical composition of the crystal phases in LiRESiO 4 was also revised to RE 10 Si 6 O 25 and/or RE 9.33 Si 6 O 24 . The discovery of oxygen-ion conductivity in these materials was confirmed when researchers noted that samples of RE 10 Si 6 O 25 , specifically, the samples without lithium, are electrically conducting. Furthermore, very high oxygen-ion conductivity in the direction parallel to c-axis was discovered after single crystals of RE 9.33 (SiO 4 ) 6 O 2 (RE = Nd, Pr, and Sm) were successfully grown. The crystal structure and defect models were also altered after the discovery of oxygen-ion conductivity. Although numerous reports related to the electrical conductivity of La 9.33+x (SiO 4 ) 6 O 2+3x/2 ceramics have appeared in the literature, clear dependences of the total conductivity on the cation nonstoichiometry (x) as well as the sintering temperature are still unclear because of large discrepancies in the reported data. Furthermore, the composition region, where the lanthanum silicate oxyapatite single phase is formed, is also still unclear because of the inconsistencies in the reported results.

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Evidence of local defects in the oxygen excess apatite La9.67(SiO4)6O2.5 from high resolution neutron powder diffraction

Cited by 45 publications

References 44 publications

Effect of the dopant nature on the conductivity of oxygen overstoichiometric oxyapatites with controlled microstructures

Effect of the dopant nature on the conductivity of oxygen overstoichiometric oxyapatites with controlled microstructures

Apatite germanates doped with tungsten: synthesis, structure, and conductivity

Research progress in nondoped lanthanoid silicate oxyapatites as new oxygen-ion conductors

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