Conduction properties of oxide ion conductor Ca12Al14O33 prepared with solution-synthesized powders

Matsuda, Motohide; Inda, Yasushi; Hisamatsu, Wakako; Yamashita, Kimihiro; Umegaki, Takao

doi:10.1007/bf00241430

Cited by 9 publications

(15 citation statements)

References 3 publications

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“…In previous reports on mayenite, more features were found in impedance spectra whereby grain boundary and bulk resistance could be distinguished. 4,5,52 In the present case with only one characteristic feature, the measured resistance represents a combined bulk and grain boundary resistance (refer to Section 4.3. for a detailed discussion). The time constants, t = RC, of the charge transport processes within bulk and across grain boundaries appear to be close together (difference smaller than one order of magnitude), so that they cannot be distinguished, or one process strongly dominates the whole electric response.…”

Section: Total Conductivity Of Anion-substituted Mayenitementioning

confidence: 99%

Novel anion conductors – conductivity, thermodynamic stability and hydration of anion-substituted mayenite-type cage compounds C₁₂A₇:X (X = O, OH, Cl, F, CN, S, N)

Eufinger

Schmidt

Lerch

et al. 2015

Phys. Chem. Chem. Phys.

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Mayenite (Ca12Al14O33) is a highly interesting functional material not only in view of its unique crystal structure as a cage compound but also for its variety of possible applications. Its ability to incorporate foreign ions into the cage structure opens the possibility to create new types of solid electrolytes and even electrides. Therefore, the conductivity of various anion substituted mayenites was measured as a function of temperature. Due to controversial reports on the stability of mayenite under specific thermodynamic conditions (dry, wet, reducing, and high temperature), a comprehensive study on the stability was performed. Mayenite is clearly not stable under dry conditions (ppm H2O < 100) at temperatures above 1050 °C, and thus, the mayenite phase vanishes from the calcium aluminate phase diagram below a minimum humidity. Two decomposition reactions were observed and are described in detail. To get further insight into the mechanism of hydration of mayenite, the conductivity was measured as a function of water vapour pressure in a range of -5 ≤ lg[pH2O/bar] ≤ -1.6 at temperatures ranging from 1000 °C ≤ θ ≤ 1200 °C. The hydration isotherms are described with high accuracy by the underlying point defect model, which is confirmed in a wide range of water vapour pressure.

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Section: Total Conductivity Of Anion-substituted Mayenitementioning

confidence: 99%

Novel anion conductors – conductivity, thermodynamic stability and hydration of anion-substituted mayenite-type cage compounds C₁₂A₇:X (X = O, OH, Cl, F, CN, S, N)

Eufinger

Schmidt

Lerch

et al. 2015

Phys. Chem. Chem. Phys.

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“…Chemical processing techniques have been used to synthesize amorphous calcium aluminate powders. [7][8][9][10][11][12][13][14][15][16][17][18] But the direct crystallization of the precursors into the pure corresponding crystalline phases is rather difficult. With one exception 18 it has never been reported by any thermal analysis.…”

Section: Introductionmentioning

confidence: 99%

Crystallization of Amorphous Precursors in the Calcia–Alumina System: A Differential Scanning Calorimetry Study

Douy

Gervais

2000

Journal of the American Ceramic Society

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Amorphous powders were synthesized by spray-drying aqueous solutions of calcium and aluminum nitrates, followed by calcination in order to completely decompose the salts. The formation of pure calcium aluminates-C 3 A, C 5 A 3 , C 12 A 7 , CA, CA 2 , and CA 6 (C ‫؍‬ CaO and A ‫؍‬ Al 2 O 3 )-has been studied by DSC and XRD. A number of compositions first crystallized to metastable structures without partitioning, i.e., without phase separation. This is the case for orthorhombic C 5 A 3 , orthorhombic CA, and ␥-Al 2 O 3 solid solution which may incorporate up to about 25 mol% CaO. o-C 5 A 3 ultimately partitioned into a mixture of C 12 A 7 and CA according to the equilibrium diagram. o-CA transformed partitionless into the stable monoclinic m-CA, and the stable CA 6 compound was obtained pure at low temperature from ␥-Al 2 O 3 solid solution through a second exotherm. Among all the calcium aluminates studied, C 3 A was the only one for which an intermediary amorphous precursor could not be obtained, CaO crystallizing as the nitrates were decomposed. Phase transitions involving metastable materials are often fast and release heat over a narrow temperature range leading to steep exothermal DSC signals even at a relatively low heating rate (5°C/min). The present results are consistent with current understanding of partitionless crystallization. They clearly show the ability of the synthesis used to achieve homogeneous mixing at the molecular level. Amorphous precursors formed in a large composition range may be advantageously used as glass models.

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“…Fully densified translucent ceramics are obtained when hydrated C12A7 powders prepared as precursors are sintered in a dry oxygen atmosphere at 1300°C. 9 The lattice symmetry of C12A7 is cubic, hence densified ceramics are expected to be optically transparent. Dissociation of water molecules at the grain-pore interface into grains which entraps hydroxide ions in the crystallographic cage, and the release of the hydroxide ions into the atmosphere during the sintering procedure are considered to play crucial roles in the pore-annihilation processes.…”

mentioning

confidence: 99%

“…Two remaining O 2− ions, referred to as "free oxygen," are entrapped in the cages in stoichiometric composition. [6][7][8][9] A fully dense body prohibiting gas penetration is necessary for the application of C12A7 within solid-oxide fuel cells. A series of oxygen radicals as well as other anionic species such as O − , O 2 − , OH − , F − , or Cl − 1,4 can occupy the cages instead of the free oxygen while maintaining charge neutrality.…”

mentioning

confidence: 99%

“…A series of oxygen radicals as well as other anionic species such as O − , O 2 − , OH − , F − , or Cl − 1,4 can occupy the cages instead of the free oxygen while maintaining charge neutrality. 9 The lattice symmetry of C12A7 is cubic, hence densified ceramics are expected to be optically transparent. For example, we recently found that C12A7 sintered in a dry oxygen atmosphere contains extremely high concentrations of active oxygen radicals O − and O 2 − , on the order of 10 20 cm −3 .…”

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confidence: 99%

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Translucent Ceramics of 12CaO · 7Al₂O₃ with Microporous Structure

2002

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We examined the densification of 12CaO и 7Al 2 O 3 (C12A7), which has a microporous lattice framework with a cavity of approximately 0.4 nm. Fully densified translucent ceramics are obtained when hydrated C12A7 powders prepared as precursors are sintered in a dry oxygen atmosphere at 1300°C. The average transmittance between 400-800 nm for 1-mm-thick samples is improved up to approximately 70% with a 48-h increase in the sintering time. Dissociation of water molecules at the grain-pore interface into grains which entraps hydroxide ions in the crystallographic cage, and the release of the hydroxide ions into the atmosphere during the sintering procedure are considered to play crucial roles in the pore-annihilation processes.12CaO и 7Al 2 O 3 (C12A7) 1-9 has a microporous crystal structure, in which a positively charged lattice framework [Ca 24 Al 28 O 64 ] 4+ contains crystallographic cages with a diameter of approximately 0.4 nm. Two remaining O 2− ions, referred to as "free oxygen," are entrapped in the cages in stoichiometric composition. 1-3 Figure 1 illustrates the structure of two neighboring vacant cages. A series of oxygen radicals as well as other anionic species such as O − , O 2 − , OH − , F − , or Cl − 1,4 can occupy the cages instead of the free oxygen while maintaining charge neutrality. C12A7 thus serves as an anion container, which gives rise to its novel characteristics, and it is regarded as a counterpart of zeolites, 10 which can entrap cationic species. For example, we recently found that C12A7 sintered in a dry oxygen atmosphere contains extremely high concentrations of active oxygen radicals O − and O 2 − , on the order of 10 20 cm −3 . These samples exhibited high oxidation reactivity. 4 The free oxygen in C12A7 is believed to be responsible for fast ionic conductivity. 6-9 A fully dense body prohibiting gas penetration is necessary for the application of C12A7 within solid-oxide fuel cells. However, the sinterability of C12A7 has been considered to be poor. For example, a relative density of only 93% was obtained by solid-state reaction at 1365°C for 16 h, 8 and a density of 95% was observed by sintering at 1350°C for 20 h using solution-synthesized powders as precursors. 9 The lattice symmetry of C12A7 is cubic, hence densified ceramics are expected to be optically transparent. The transparency will be valuable in investigating the cage content spectroscopically, as well as in applications such as optical windows for light sources. We report here the successful preparation of fully dense translucent ceramics of C12A7.The starting materials were CaCO 3 and ␥-Al 2 O 3 powders (99.99% purity, Kojundo Chemical Laboratory, Japan). To obtain the C12A7 single phase, 0.1 mol% excess CaO was added to the mixture with a molar ratio of 12:7. The excess CaO may play a role in compensating Al 2 O 3 powder inevitably included during the milling process described below. The mixture was reacted at 1300°C for 12 h in air to form C12A7. The product was crushed in ethanol solvent (99.5% purity, residual H 2 ...

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Conduction properties of oxide ion conductor Ca12Al14O33 prepared with solution-synthesized powders

Cited by 9 publications

References 3 publications

Novel anion conductors – conductivity, thermodynamic stability and hydration of anion-substituted mayenite-type cage compounds C₁₂A₇:X (X = O, OH, Cl, F, CN, S, N)

Novel anion conductors – conductivity, thermodynamic stability and hydration of anion-substituted mayenite-type cage compounds C₁₂A₇:X (X = O, OH, Cl, F, CN, S, N)

Crystallization of Amorphous Precursors in the Calcia–Alumina System: A Differential Scanning Calorimetry Study

Translucent Ceramics of 12CaO · 7Al₂O₃ with Microporous Structure

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Conduction properties of oxide ion conductor Ca12Al14O33 prepared with solution-synthesized powders

Cited by 9 publications

References 3 publications

Novel anion conductors – conductivity, thermodynamic stability and hydration of anion-substituted mayenite-type cage compounds C12A7:X (X = O, OH, Cl, F, CN, S, N)

Novel anion conductors – conductivity, thermodynamic stability and hydration of anion-substituted mayenite-type cage compounds C12A7:X (X = O, OH, Cl, F, CN, S, N)

Crystallization of Amorphous Precursors in the Calcia–Alumina System: A Differential Scanning Calorimetry Study

Translucent Ceramics of 12CaO · 7Al2O3 with Microporous Structure

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Novel anion conductors – conductivity, thermodynamic stability and hydration of anion-substituted mayenite-type cage compounds C₁₂A₇:X (X = O, OH, Cl, F, CN, S, N)

Novel anion conductors – conductivity, thermodynamic stability and hydration of anion-substituted mayenite-type cage compounds C₁₂A₇:X (X = O, OH, Cl, F, CN, S, N)

Translucent Ceramics of 12CaO · 7Al₂O₃ with Microporous Structure