Interstitial oxygen in oxygen-stoichiometric apatites

León‐Reina, Laura; Losilla, Enrique R.; Martı́nez-Lara, M.; Bruque, S.; Llobet, Anna; Sheptyakov, Denis; Aranda, Miguel A. G.

doi:10.1039/b503374h

Cited by 119 publications

(138 citation statements)

References 45 publications

Supporting

Mentioning

118

Contrasting

Unclassified

Order By: Relevance

“…1(b). Such an interaction between SiO 4 and interstitial oxygen ion was also pointed out experimentally by 29 Si NMR measurements for stoichiometric La 9.33 (SiO 4 ) 6 O 2 and oxygen-excess La 9.67 (SiO 4 ) 6 -O 2.5 .…”

Section: Low-energy Interstitial Sitessupporting

confidence: 65%

Ionic conduction mechanisms of apatite-type lanthanum silicate and germanate from first principles

Matsunaga

2017

J. Ceram. Soc. Japan

View full text Add to dashboard Cite

Ionic conduction mechanisms in apatite-type lanthanum silicate and germanate studied by first-principles calculations were reviewed, along with the ones previously proposed by experiments and atomistic simulations. It was found that the most stable interstitial oxygen sites in La 10 (SiO 4 ) 6 O 3 are located at the vicinity of the O4 column and the metastable sites are present between SiO 4 tetrahedra. In contrast, La 10 (GeO 4 ) 6 O 3 showed the most stable sites between GeO 4 tetrahedra, forming Ge 2 O 9 units. These can reasonably explain interstitial sites reported experimentally. The fundamental mechanism for ionic conduction in both systems is the interstitialcy mechanism, where interstitial oxygen ions and oxygen ions at regular lattice sites undergo cooperative motion through the lattices. In particular, the interstitialcy mechanism via Si/GeO 4 tetrahedra takes place by sequential bondforming and bond-breaking events between Si/Ge and oxygen ions, and play an important role to realize rapid ionic conduction.

show abstract

Section: Low-energy Interstitial Sitessupporting

confidence: 65%

Ionic conduction mechanisms of apatite-type lanthanum silicate and germanate from first principles

Matsunaga

2017

J. Ceram. Soc. Japan

View full text Add to dashboard Cite

show abstract

“…Experimental studies have provided confirmation of this position, with Leon-Reina et al showing occupation of a similar site in neutron diffraction studies of the La 9.33+x (Si/Ge) 6 [21][22][23][24]. Moreover, the modelling results further suggested a complex sinusoidal conduction pathway down the channels.…”

Section: Introductionmentioning

confidence: 69%

“…In terms of doping studies, a wide range of dopants have been reported [17,[23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39], Rare earth site: Mg, Ca, Sr, Ba, Bi, Mn, Co, Ni, Cu Si site: Ge, Ti, P, B, Al, Ga, Mn, Co, Fe, Mg, Zn, Ni, Cu Initial studies showed that doping with lower valent ions, e.g. B 3+ , Al 3+ , Ga 3+ , on the Si site, while maintaining oxygen stoichiometry, i.e.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2007

View full text Add to dashboard Cite

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.

show abstract

“…Their structure may be described in terms of an (Ln/A) 4-x (Si/GeO 4 ) 6 framework, with the remaining (La/A) 6 O 2 units accommodated in the channels within the 4 framework. In these systems, the oxide ion conduction process has been shown to proceed via a mechanism involving interstitial oxide ions, which are present as a result of either oxygen hyperstoichiometry (x>0) in La 8+x Sr 2-x (Si/Ge) 6 With regard to the location of the interstitial oxide ions, computer modelling studies have predicted that for the silicates the most favourable interstitial oxide ion site is at the periphery of the oxide ion channels neighbouring the SiO 4 groups, which has been supported by neutron diffraction, 29 Si NMR, and Raman studies [14,15,17,27,36]. For the germanates, both modelling and neutron diffraction studies also indicate an interstitial position neighbouring the GeO 4 tetrahedra, although in this case the interstitial oxide ion is more closely associated, leading to five coordinate Ge [21,26].…”

Section: Introductionmentioning

confidence: 85%

Formation of apatite oxynitrides by the reaction between apatite-type oxide ion conductors, La8+xSr2−x(Si/Ge)6O26+x/2, and ammonia

Orera

Headspith

Apperley

et al. 2009

Journal of Solid State Chemistry

View full text Add to dashboard Cite

Following growing interest in the use of ammonia as a fuel in Solid Oxide Fuel Cells (SOFCs), we have investigated the possible reaction between the apatite silicate/germanate electrolytes, La 8+x Sr 2-x (Si/Ge) 6 O 26+x/2 , and NH 3 gas. We examine how the composition of the apatite phase affects the reaction with ammonia. For the silicate series, the results showed a small degree of N incorporation at 600 ○ C, while at higher temperatures (800 ○ C), substantial N incorporation was observed. For the germanate series, partial decomposition was observed after heating in ammonia at 800 ○ C, while at the lower temperature (600 ○ C), significant N incorporation was observed. For both series, the N content in the resulting apatite oxynitride was shown to increase with increasing interstitial oxide ion content (x) in the starting oxide. The results suggest that the driving force for the nitridation process is to remove the interstitial anion content, such that for the silicates the total anion (O+N) content in the oxynitrides approximates to 26.0, the value for an anion stoichiometric apatite. For the germanates, lower total anion contents are observed in some cases, consistent with the ability of the germanates to accommodate anion vacancies. The removal of the mobile interstitial oxide ions on nitridation suggests problems with the use of apatite-type electrolytes in SOFCs utilising NH 3 at elevated temperatures.

show abstract

Interstitial oxygen in oxygen-stoichiometric apatites

Cited by 119 publications

References 45 publications

Ionic conduction mechanisms of apatite-type lanthanum silicate and germanate from first principles

Ionic conduction mechanisms of apatite-type lanthanum silicate and germanate from first principles

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

Formation of apatite oxynitrides by the reaction between apatite-type oxide ion conductors, La8+xSr2−x(Si/Ge)6O26+x/2, and ammonia

Contact Info

Product

Resources

About