Dopant substitution and oxygen migration in the complex perovskite oxide Ba3CaNb2O9: A computational study

Ruiz‐Trejo, Enrique; Souza, Roger A. De

doi:10.1016/j.jssc.2005.04.002

Cited by 20 publications

(10 citation statements)

References 39 publications

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“…It has been noted previously from computational investigations on proton-conducting perovskite-type oxide materials that a lower oxygen-to-oxygen ion distance results in a smaller value of the activation energy for the proton jump. 22,23 Hereby the same concept for proton conduction is extended to phosphate materials. A qualitative graphical demonstration of the above statement is presented in Fig.…”

Section: Introductionmentioning

confidence: 99%

Conductivity Enhancement in Lanthanum Phosphates

Phadke

Nino

2011

Journal of the American Ceramic Society

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Current proton exchange membranes (PEM) are based on polymeric materials such as perfluorosulfonic acid (Nafion™), which have an upper limit to their temperature of operation (<100°C). To overcome this limitation, ceramic PEM materials are being investigated for transportation applications, where operating temperatures in the range of 200°–600°C are desired. In this study, the conductivity behavior of lanthanum orthophosphate (LaPO4) has been compared and contrasted with lanthanum ultraphosphate (LaP5O14) in order to better understand crystal structure—proton conduction relationships in ceramic materials. The conductivity of the lanthanum phosphates (doped and undoped) was measured using impedance spectroscopy in the temperature range 300°–600°C. The conductivity of 5 mol% Sr2+‐doped LaP5O14 (1.01 × 10−4 S/cm, 600°C) was found to be an order of magnitude higher than similarly doped LaPO4 (7.00 × 10−6 S/cm, 600°C), which is a well‐investigated proton conducting material. In addition, it was observed that the activation energy for protonic conduction was much lower for doped LaP5O14 (0.80 ± 0.01 eV) as compared with LaPO4 (1.09 ± 0.01 eV). A hypothesis relating the oxygen‐to‐oxygen ion distance in a material to the activation energy for proton conduction is presented and the experimental results obtained have been critically examined on the basis of the hypothesis and other relevant literature. From this analysis, it is shown that the condensed nature of the phosphate anion in LaP5O14 can provide low‐energy avenues for proton transport within the material leading to enhanced conductivity in the material. Limitations of the currently proposed model for proton conduction along with some other plausible explanations for the conductivity enhancement have also been discussed.

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Section: Introductionmentioning

confidence: 99%

Conductivity Enhancement in Lanthanum Phosphates

Phadke

Nino

2011

Journal of the American Ceramic Society

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“…It is important to emphasize that various effects such as bond lengths or the very nature of the bond will change the vibration energies and hence the frequencies and wave numbers. CaO 6 octahedra are very different from NbO 6 both in terms of size (3.35 Å vs 2.8 Å [5]), bond nature and crystallographic position yet a clear consequence of the presence of CaO 6 and NbO 6 oscillators is not obvious. Nonetheless, a very clear trend between the energy of vibration and the (pseudocubic) lattice parameter can be observed for the series studied here and more complex perovskites as shown in Fig.…”

Section: Raman Analysismentioning

confidence: 95%

“…The energy of a polaron is highly dependent upon the energy involved in the deformation of the surrounding lattice. This is of great relevance to the description of the BCN system, since there are two types of Nb sites in the cubic structure (space group Fm-3 m) with very different characteristics in terms of distance to next nearest neighbours and energy of substitution [5]. If the samples are completely or partially cubic, there must be two energies associated with each type of free polaron, one of them is at 2.39 eV as mentioned above.…”

Section: Electronic Defectsmentioning

confidence: 98%

“…In particular, Ba 3 Ca 1+x Nb 2-x O 9-δ with x 00.18 (labeled BCN18) exhibits considerable levels of proton conduction even though hydrogen is not a constituent of the crystal lattice [3][4][5][6]. This and other complex perovskite families have a considerable potential as materials for fuel cells since the electrolytical properties can be finely tuned by modifying the Ca/Nb ratio to generate oxygen vacancies, by selecting the basicity of the contituent cations (Ba, Ca, Sr) to promote the incorporation of water and by controling the electronic conductivity of the family with a suitable choice of cations (Nb, Ta).…”

Section: Introductionmentioning

confidence: 99%

“…The cubic and hexagonal structures of the complex perovskite Ba 3 CaNb 2 O 9 (labelled BCN) have been described elsewhere [5]. It is however, not yet clear to what extent and in what conditions the members of the family display a cubic or an hexagonal symmetry.…”

Section: Introductionmentioning

confidence: 99%

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Influence of the calcium excess in the structural and spectroscopic properties of the complex perovskite Ba3CaNb2O9

et al. 2012

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The effects of the change in the Ca/Nb ratio in the structure and spectroscopic properties of the solid solution Ba 3 Ca 1+x Nb 2-x O 9-δ with x00-0.25 are investigated. The solid solution undergoes a transition from an hexagonal phase (2:1 order) to a cubic phase (1:1 order) with increasing calcium content as indicated by X-Ray diffraction and Raman. The calcium excess matches with a gradual increase in blue colour due to a reduction at the high temperatures of sintering. Optical absorption experiments showed that there are different absorption bands in the region 0.45-4.5 eV corresponding tentatively to OH vibrations, polarons and monovalent oxygen vacancies. The series properties change gradually with calcium excess with the exception of Ba 3 Ca 1.18 Nb 1.82 O 9-δ that showed a slight change attributable to the presence of protons in the lattice. These changes can be used to quantify protons in complex perovskites.

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