Defect chemistry and oxygen ion migration in the apatite-type materials La9.33Si6O26 and La8Sr2Si6O26

Tolchard, Julian R.; Islam, M. Saïful; Slater, Peter R.

doi:10.1039/b302748c

Cited by 266 publications

(359 citation statements)

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“…This coupled with the high thermal displacement parameters indicates significant displacement of oxygens into interstitial sites. Difference fourier maps were investigated to locate the exact positions of the interstitial sites, and indicated small regions of unfitted scattering along the channels near to the channel centre, along with regions at the periphery of the channels in positions similar to the favourable interstitial site predicted by our modelling studies of La 9.33 Si 6 O 26 [19,20], and subsequently reported in neutron diffraction studies of La 9.33+x (Si/Ge) 6 O 26+3x/2 by Leon-Reina et al [21][22][23]. However, attempts to refine occupancy in these sites were unsuccessful, which may be due to the displaced oxygens being distributed over not just one, but a range of interstitial sites, leading to low occupancies for each site.…”

Section: Discussionmentioning

confidence: 90%

“…The modelling studies identified a new energetically favourable interstitial oxide ion position at the periphery of the oxide ion channels, in the vicinity of the SiO 4 groups [19,20].…”

Section: Introductionmentioning

confidence: 99%

“…A well established three-body term for the angle-dependant [SiO 4 ] tetrahedral unit was used [19,20]. Because charged defects will polarise other ions in the lattice, it is important to include a good description of ionic polarisability in the model.…”

Section: Introductionmentioning

confidence: 99%

“…Interatomic potentials were transferred directly from our previous study of La 9.33 Si 6 O 26 , which accurately reproduce the observed complex structure [19,20]. For this work, calculations were based upon a 1x1x3 supercell (124 atoms) of the …”

Section: Introductionmentioning

confidence: 99%

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Neutron diffraction and atomistic simulation studies of Mg doped apatite-type oxide ion conductors

et al. 2007

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In this paper, detailed studies of the effect of Mg doping in the apatite-type oxide ion conductor La 9.33 Si 6 O 26 are reported. Mg is confirmed as an ambi-site dopant, capable of substituting for both La and Si, depending on the starting composition. A large enhancement in the conductivity is observed for Si site substitution, with a reduction for substitution on the La site. Neutron powder diffraction studies show that in agreement with cation size expectations, an enlargement of the unit cell is observed on Mg substitution for Si, with a corresponding increase in the size of the tetrahedral sites. For Mg substitution on the La site, a contraction of the unit cell is observed, and the neutron diffraction results indicate that there is preferential occupancy of Mg on the La2 (1/3, 2/3, ≈0.5) site. Atomistic simulation studies show significant local structural changes affecting the oxide ion channels in both cases. Mg doping on the Si site leads to a local expansion of the channels, while doping on the La site results in a large displacement of the silicate O4 site, such that it encroaches the oxide ion channels. The observed differences in conductivities are discussed with respect to these observations.

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Section: Discussionmentioning

confidence: 90%

“…The modelling studies identified a new energetically favourable interstitial oxide ion position at the periphery of the oxide ion channels, in the vicinity of the SiO 4 groups [19,20].…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Neutron diffraction and atomistic simulation studies of Mg doped apatite-type oxide ion conductors

et al. 2007

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“…The low conductivity is consistent with previous results that for high conductivity in these apatite systems, nonstoichiometry in the form of cation vacancies and/or oxygen excess is required, however the high value of U 33 might suggest a high conductivity should be observed. Thus arguments that the high conductivity in apatite systems can be related to the high U 33 for the channel oxygen seem to be simplistic and other features, such as the silicate network as predicted by modelling studies 13,14 , must play a key role.…”

Section: -Structural Determinationmentioning

confidence: 99%

Structural studies of apatite-type oxide ion conductors doped with cobalt

et al. 2005

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All compositions were shown to possess the hexagonal apatite structure, and the results confirmed that cobalt can be doped onto both the La and Si sites within the structure depending on the starting composition. The Co doping is shown to cause considerable local distortions within the apatite structure. In the case of Si site doping two compositions showed anisotropic peak broadening, which has been attributed to incommensurate ordering of oxygen within the apatite channels.

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Oxygen Ion‐Conducting Materials

Хартон

Marques

Kilner

et al. 2009

Solid State Electrochemistry I

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Oxygen ionic and mixed ionic-electronic conductors find important applications in solid-state electrochemical devices, including sensors, solid oxide fuel cells, hightemperature electrolyzers, and oxygen separation membranes. This chapter presents a brief overview of oxide phases with high diffusivity of O 2À anions, providing an introduction to this fascinating topic. Particular emphasis is centered on the comparative analysis of ionic and electronic conductivity variations in the major groups of solid oxide electrolytes and mixed conductors, such as perovskite-and fluorite-related compounds, apatite-type silicates, and derivatives of g-Bi 4 V 2 O 11 and b-La 2 Mo 2 O 9 . The defect chemistry mechanisms relevant to the oxygen ion migration processes are briefly discussed. IntroductionTechnologies based on the use of high-temperature electrochemical cells with oxygen anion-or mixed-conducting ceramics provide important advantages with respect to the conventional industrial processes [1][2][3][4][5][6][7][8]. In particular, solid oxide fuel cells (SOFCs) are considered as alternative electric power generation systems due to high energy-conversion efficiency, fuel flexibility, and environmental safety [1][2][3]. Dense ceramic membranes with mixed oxygen-ionic and electronic conductivity have an infinite theoretical separation factor with respect to oxygen, and can be used for gas separation and the partial oxidation of light hydrocarbons [4,5,7,8] (these and other applications are reviewed in Chapters 12 and 13). For all types of electrochemical cells, the key properties which determine the use of a material are the partial ionic and electronic conductivities. As an example, solid electrolytes for SOFCs, oxygen pumps and electrochemical sensors should exhibit a maximum oxygen ionic conductivity, while the electronic transport should be minimal. In contrast, for SOFC electrodes Solid State Electrochemistry I: Fundamentals, Materials and their Applications. Edited by Vladislav V. Kharton

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Defect chemistry and oxygen ion migration in the apatite-type materials La9.33Si6O26 and La8Sr2Si6O26

Abstract: ] tetrahedra to assist in the facile conduction of oxygen interstitial ions. In general, the modelling study confirms that the high ionic conductivity in silicate-based apatites (with oxygen excess or cation vacancies) is mediated by oxygen interstitial migration.

Cited by 266 publications

References 24 publications

Neutron diffraction and atomistic simulation studies of Mg doped apatite-type oxide ion conductors

Neutron diffraction and atomistic simulation studies of Mg doped apatite-type oxide ion conductors

Structural studies of apatite-type oxide ion conductors doped with cobalt

Oxygen Ion‐Conducting Materials

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