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Crystal structure of Re‐substituted lanthanum tungstate La 5.4 W 1− y Re y O 12–δ (0 ≤ y ≤ 0.2) studied by 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 - 2016
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/s1600576716011523
Subject(s) - tungstate , lanthanum , crystallography , crystal structure , neutron diffraction , thermogravimetry , chemistry , single crystal , analytical chemistry (journal) , inorganic chemistry , chromatography
A precise determination of sample composition and water uptake of La 6− x WO 12−δ (0.4 ≤ x ≤ 0.8) and Re‐substituted La 5.4 W 1− y Re y O 12−δ (0 ≤ y ≤ 0.2) lanthanum tungstate is carried out. Sample compositions and water uptake were determined by electron probe micro‐analysis and thermogravimetry, respectively. A single‐phase region of Re‐substituted lanthanum tungstates is reported. The crystal structure of two selected specimens produced by the citrate‐complexation route based on the Pechini method, namely La 5.4 WO 12−δ and La 5.4 W 0.8 Re 0.2 O 12−δ , was investigated by neutron diffraction in the temperature range 1.5 ≤ T ≤ 1200 K. The structural model for lanthanum tungstates is validated, according to which the Wyckoff site shared by La and W ( space group, 24 d site) is split with half‐site occupancies ( space group, 48 h site). Replacement of W by up to 20 mol% Re does not change the lattice structure, and Re atoms substitute for W statistically in both 4 a and 48 h Wyckoff sites of the space group, as shown by combining the average neutron scattering length procedure, thermogravimetry and electron probe micro‐analysis. Using the Willis and Pryor approach to anisotropic displacement parameters it is shown that the remaining static disorder in the unit cell found in La 5.4 WO 12−δ and La 5.4 W 0.8 Re 0.2 O 12−δ structures is comparable, when the space group with split 48 h site is employed. Through the estimation of the Debye temperature for both compounds, extracted from the analysis of thermal expansion coefficients and from the Willis and Pryor approach, anion anharmonic vibrations like those in yttria‐stabilized zirconia are proven to exist in LaWO for the first time.