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Crystal structure of Mo‐substituted lanthanum tungstate La 5.4 W 1− y Mo y O 12−δ (0 ≤ y ≤ 0.2) studied by X‐ray and neutron diffraction
Author(s) -
Fantin Andrea,
Scherb Tobias,
Seeger Janka,
Schumacher Gerhard,
Gerhards Uta,
Ivanova Mariya E.,
Meulenberg Wilhelm A.,
Dittmeyer Roland,
Banhart John
Publication year - 2019
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576719009385
Subject(s) - lanthanum , crystallography , tungstate , crystal structure , neutron diffraction , bond length , chemistry , x ray crystallography , single crystal , diffraction , inorganic chemistry , physics , optics
A determination of the detailed crystal structure of an Mo‐substituted lanthanum tungstate series, La 6− x W 1− y Mo y O 12−δ (0 ≤ y ≤ 0.2, δ is the oxygen deficiency), is presented. Material of composition La 5.4 W 0.8 Mo 0.2 O 12−δ ( y = 0.2) produced by the citrate‐complexation route based on the Pechini method was investigated by high‐resolution X‐ray diffraction and neutron diffraction in the temperature range 10 ≤ T ≤ 298 K. The results are compared with a non‐substituted material La 5.4 WO 12−δ . A structural model established earlier for lanthanum tungstates and Re‐substituted lanthanum tungstates is confirmed, according to which the Wyckoff site shared by La and W is split with half site occupancies ( space group, 48 h site) and also accommodates Mo atoms. Substitution of W by up to 20 mol% Mo does not change the face‐centred cubic lattice: Mo atoms substitute W statistically on both 4 a and 48 h Wyckoff sites of the crystal structure, which is described by the space group. These results were obtained from the combination of the average neutron‐scattering length and average X‐ray scattering power procedures with electron‐probe micro‐analysis. The temperature dependence of bond lengths in dry and wet (D 2 O) conditions shows that vacant oxygen sites are located on the 32 f Wyckoff sites also in Mo‐substituted lanthanum tungstates, and that the bond lengths between La on 4 b and O on 32 f increase with increasing p O 2 and p D 2 O, reflecting the filling of oxygen vacancies and the increase in coordination of La on 4 b .