Crystal structure of Re‐substituted lanthanum tungstate La5.4W1−yReyO12–δ (0 ≤ y ≤ 0.2) studied by neutron diffraction. Issue 5 (23rd August 2016)

• Record Type: Journal Article
• Authors: Fantin, Andrea; Scherb, Tobias; Seeger, Janka; Schumacher, Gerhard; Gerhards, Uta; Ivanova, Mariya E.; Meulenberg, Wilhelm A.; Dittmeyer, Roland; Banhart, John
• Is Part Of: Journal of applied crystallography. Volume 49:Issue 5(2016)
• Page Start: 1544
• Page End: 1560
• Publication Date: 2016-08-23
• Subjects: Re‐substituted lanthanum tungstates -- La5.6WO12−δ -- anharmonic vibrations -- anisotropic displacement parameters -- mixed protonic electronic conductors -- neutron diffraction; Crystallography -- Periodicals; 548.05
• DOI: 10.1107/S1600576716011523
• Languages: English
• ISSNs: 0021-8898

Abstract

Abstract : This work describes in detail the structure of nonsubstituted and Re‐substituted lanthanum tungstates studied through neutron diffraction as a function of temperature between 1.5 and 1200 K. Thermogravimetry and electron probe micro‐analysis techniques were employed in combination with neutron diffraction to locate Re atoms in the LaWO crystal structure. Abstract : A precise determination of sample composition and water uptake of La6− x WO12−δ (0.4 ≤ x ≤ 0.8) and Re‐substituted La5.4 W1− y Re y O12−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 La5.4 WO12−δ and La5.4 W0.8 Re0.2 O12−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 La5.4 WO12−δ and La5.4 W0.8 Re0.2 O12−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.