Thermal evolution of the crystal structure of proton conducting BaCe0.8Y0.2O3−δ from high-resolution neutron diffraction in dry and humid atmosphere

Andersson, Annika Kristina Eriksson; Selbach, Sverre M.; Grande, Tor; Knee, Christopher S.

doi:10.1039/c4dt03948c

Cited by 31 publications

(26 citation statements)

References 53 publications

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“…Fourier nuclear-density maps were calculated for the 10 K data with incident neutron wavelengths of both 1.04 and 1.594 Å in order to locate missing nuclear-scattering density arising from the deuterons, as has been performed for a number of oxide proton conductors 31,32 . Inspection of the density maps at both acquired resolutions, such as those illustrated in Fig.…”

Section: Location Of Deuteron Sitesmentioning

confidence: 99%

Phase Transitions, Chemical Expansion, and Deuteron Sites in the BaZr_0.7Ce_0.2Y_0.1O_3−δ Proton Conductor

et al. 2016

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The crystal structure of the technologically relevant, high-temperature proton conductor BaZr0.7Ce0.2Y0.1O3- (BZCY72) has been studied by high-resolution neutron powder diffraction performed on a deuterated sample in the temperature range 10-1173 K, complemented with synchrotron X-ray diffraction in the range RT-1173 K. A volume discontinuity on heating indicates a first-order phase transition from orthorhombic (space group Imma) to rhombohedral symmetry ( 3 Rc ) between 85 and 150 K. A further transition to cubic symmetry ( 3 Pm m ) takes place at ~ 570 K, indicated to be second order from the temperature dependence of the octahedral tilt angle. The stability field of the cubic phase was extended on cooling in the dehydrated state to 85 K. Expansion/contraction of the unit-cell volume on heating in low vacuum and air, respectively observed by neutron diffraction and synchrotron X-ray diffraction, was described with a point-defect model involving the temperature dependence of the water content and thermal expansion. Isotropic strain in the hydrated state is apparent on analysis of the broadening of the neutron-diffraction reflections during heating and cooling cycles. Rietveld refinement of the low-temperature neutron data and Fourier nuclear-density maps were employed to locate the deuterium position at a distance of ~ 0.90 Å from the bonding oxygen at 10 K.

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Section: Location Of Deuteron Sitesmentioning

confidence: 99%

Phase Transitions, Chemical Expansion, and Deuteron Sites in the BaZr_0.7Ce_0.2Y_0.1O_3−δ Proton Conductor

et al. 2016

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“…A considerable strain induced stress during chemical expansion due to hydration/dehydration was recently addressed for BZY-materials. 51,52 During operation of a fuel cell the level of the stress will additionally depend on the gradient in the concentration of the water or protons as they diffuse from the surface to the interior of a material. The stress induced at the surface during reaction with CO2 is reflected by the reduced fracture toughness reported here.…”

Section: Mechanical Stability Of Bazr1-xyxo3-x/2 and Bace02zr07y01mentioning

confidence: 99%

Effect of CO₂ Exposure on the Chemical Stability and Mechanical Properties of BaZrO₃‐Ceramics

et al. 2016

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The reactivity of BaZrO3 with CO2 has been addressed as one of the major challenges with BaZrO3-based electrolytes in proton ceramic fuel cells. Here, we present a study of the effect of CO2 exposure of BaZrO3-materials at elevated temperatures. Dense BaZr1-xYxO3-δ (x = 0, 0.05, 0.1, 0.2) and BaCe0.2Zr0.7Y0.1O2.95 ceramics were prepared by conventional sintering of powder prepared by spray pyrolysis. The Vickers indentation method was used to determine the hardness and estimate the fracture toughness of pristine materials as well as the corresponding materials exposed to CO2. Formation of BaCO3 on the surface of exposed ceramics was confirmed by X-ray diffraction and electron microcopy. The reaction resulted in formation of Ba-deficient perovskite at the exposed surface. The reaction with CO2 was most pronounced at 650 ºC compared to the other temperatures applied in the study. The reactivity was also shown to depend on the Y-content and the grain size and was most pronounced for BaZr0.9Y0.1O3-δ. The reaction with CO2 was observed to have a profound effect on the fracture toughness of the ceramics, demonstrating a depression of the mechanical stability of the materials. The results are discussed with respect to the chemical and mechanical stability of BaZrO3 materials, with particular emphasis on the composition and grain size.

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“…Experimental methods allowing the processes (hydration, dehydration and response under controlled gas flows) and relevant structural parameters (structural changes, lattice parameters and possible diffusion pathways) to be investigated in situ over a wide temperature range are likely to be an invaluable asset. A recent example where this methodology was applied is on a leading proton conducting perovskite, BaCe 0.8 Y 0.2 O 3−δ , 58 where the phase stability fields of the cubic and orthorhombic structures at operational temperatures were shown to be highly dependent on the humidity, from high resolution NPD investigations. These findings were explained by an enhanced tendency for tilting of the oxygen octahedra in the hydrated (deuterated) state.…”

Section: Discussionmentioning

confidence: 99%

The influence of cation ordering, oxygen vacancy distribution and proton siting on observed properties in ceramic electrolytes: the case of scandium substituted barium titanate

et al. 2017

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The origin of the 2-order of magnitude difference in the proton conductivity of the hydrated forms of hexagonal and cubic oxygen deficient BaScTiO (x = 0.2 and x = 0.7) was probed using a combination of neutron diffraction and density functional theory techniques to support published X-ray diffraction, conductivity, thermogravimetric and differential scanning calorimetry studies. Cation ordering is found in the 6H structure type (space group P6/mmc) adopted by BaScTiO with scandium preferentially substituting in the vertex sharing octahedra (2a crystallographic site) and avoiding the face-sharing octahedra (4f site). This is coupled with oxygen vacancy ordering in the central plane of the face-sharing octahedra (O1 site). In BaScTiO a simple cubic perovskite (space group Pm3[combining macron]m) best represents the average structure from Rietveld analysis with no evidence of either cation ordering or oxygen vacancy ordering. Significant diffuse scattering is observed, indicative of local order. Hydration in both cases leads to complete filling of the available oxygen vacancies and permits definition of the proton sites. We suggest that the more localised nature of the proton sites in the 6H structure is responsible for the significantly lower proton conduction observed in the literature. Within the 6H structure type final model, proton diffusion requires a 3-step process via higher energy proton sites that are unoccupied at room temperature and is also likely to be anisotropic whereas the highly disordered cubic perovskite proton position allows 3-dimensional diffusion by well-described modes. Finally, we propose how this knowledge can be used to further materials design for ceramic electrolytes for proton conducting fuel cells.

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Thermal evolution of the crystal structure of proton conducting BaCe_0.8Y_0.2O_3−δ from high-resolution neutron diffraction in dry and humid atmosphere

Cited by 31 publications

References 53 publications

Phase Transitions, Chemical Expansion, and Deuteron Sites in the BaZr_0.7Ce_0.2Y_0.1O_3−δ Proton Conductor

Phase Transitions, Chemical Expansion, and Deuteron Sites in the BaZr_0.7Ce_0.2Y_0.1O_3−δ Proton Conductor

Effect of CO₂ Exposure on the Chemical Stability and Mechanical Properties of BaZrO₃‐Ceramics

The influence of cation ordering, oxygen vacancy distribution and proton siting on observed properties in ceramic electrolytes: the case of scandium substituted barium titanate

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Thermal evolution of the crystal structure of proton conducting BaCe0.8Y0.2O3−δ from high-resolution neutron diffraction in dry and humid atmosphere

Cited by 31 publications

References 53 publications

Phase Transitions, Chemical Expansion, and Deuteron Sites in the BaZr0.7Ce0.2Y0.1O3−δ Proton Conductor

Phase Transitions, Chemical Expansion, and Deuteron Sites in the BaZr0.7Ce0.2Y0.1O3−δ Proton Conductor

Effect of CO2 Exposure on the Chemical Stability and Mechanical Properties of BaZrO3‐Ceramics

The influence of cation ordering, oxygen vacancy distribution and proton siting on observed properties in ceramic electrolytes: the case of scandium substituted barium titanate

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Product

Resources

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Thermal evolution of the crystal structure of proton conducting BaCe_0.8Y_0.2O_3−δ from high-resolution neutron diffraction in dry and humid atmosphere

Phase Transitions, Chemical Expansion, and Deuteron Sites in the BaZr_0.7Ce_0.2Y_0.1O_3−δ Proton Conductor

Phase Transitions, Chemical Expansion, and Deuteron Sites in the BaZr_0.7Ce_0.2Y_0.1O_3−δ Proton Conductor

Effect of CO₂ Exposure on the Chemical Stability and Mechanical Properties of BaZrO₃‐Ceramics