In:
Journal of Applied Crystallography, International Union of Crystallography (IUCr), Vol. 53, No. 6 ( 2020-12-01), p. 1471-1483
Kurzfassung:
Mixed ionic electronic conducting ceramics Nd 6− y WO 12−δ (δ is the oxygen deficiency) provide excellent stability in harsh environments containing strongly reactive gases such as CO 2 , CO, H 2 , H 2 O or H 2 S. Due to this chemical stability, they are promising and cost-efficient candidate materials for gas separation, catalytic membrane reactors and protonic ceramic fuel cell technologies. As in La 6− y WO 12−δ , the ionic/electronic transport mechanism in Nd 6− y WO 12−δ is expected to be largely controlled by the crystal structure, the conclusive determination of which is still lacking. This work presents a crystallographic study of Nd 5.8 WO 12−δ and molybdenum-substituted Nd 5.7 W 0.75 Mo 0.25 O 12−δ prepared by the citrate complexation route. High-resolution synchrotron and neutron powder diffraction data were used in combined Rietveld refinements to unravel the crystal structure of Nd 5.8 WO 12−δ and Nd 5.7 W 0.75 Mo 0.25 O 12−δ . Both investigated samples crystallize in a defect fluorite crystal structure with space group Fm 3 m and doubled unit-cell parameter due to cation ordering. Mo replaces W at both Wyckoff sites 4 a and 48 h and is evenly distributed, in contrast with La 6− y WO 12−δ . X-ray absorption spectroscopy as a function of partial pressure p O 2 in the near-edge regions excludes oxidation state changes of Nd (Nd 3+ ) and W (W 6+ ) in reducing conditions: the enhanced hydrogen permeation, i.e. ambipolar conduction, observed in Mo-substituted Nd 6− y WO 12−δ is therefore explained by the higher Mo reducibility and the creation of additional – disordered – oxygen vacancies.
Materialart:
Online-Ressource
ISSN:
1600-5767
DOI:
10.1107/S1600576720012698
DOI:
10.1107/S1600576720012698/kc5116sup1.cif
Sprache:
Unbekannt
Verlag:
International Union of Crystallography (IUCr)
Publikationsdatum:
2020
ZDB Id:
2020879-0
