Room temperature structure and transport properties of the incommensurate modulated LaNb0.88W0.12O4.06. Issue 5 (11th December 2018)

• Record Type: Journal Article
• Authors: Li, Cheng; Pramana, Stevin S.; Skinner, Stephen J.
• Is Part Of: Dalton transactions. Volume 48:Issue 5(2019)
• Page Start: 1633
• Page End: 1646
• Publication Date: 2018-12-11
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c8dt03958e
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Cation ordering in the modulated La(Nb, W)O4+ d phases has been demonstrated and the role of W in inducing occupancy modulation to this phase discussed. This is linked with the oxide ion transport, highlighting that modulated complex structures are viable candidates for ion conducting applications. Abstract : The crystal structure of a (3 + 2)D incommensurate modulated LaNb0.88 W0.12 O4.06 phase, a novel oxygen ionic conductor, is refined using a combination of synchrotron X-ray diffraction and electron diffraction data. The superspace group I 2/ c ( α 1 0 γ 1 )00( α 2 0 γ 2 )00 ( a = 5.4131(1) Å, b = 11.6432(2) Å, c = 5.2963(1) Å, β = 91.540(1)°, q 1 = 0.2847(5) a * + 0.1098(9) c * and q 2 = −0.1266(9) a* + 0.2953(1) c* ) was chosen for the refinement. Similar to other scheelite type modulated structures, the modulation of LaNb0.88 W0.12 O4.06 stems from the cation occupancy ordering in the xz plane. To facilitate the modulated cation sub-lattice, and to compensate for the difference in their size and charge, the B site polyhedra are distorted by stretching the B–O bond lengths. Consequently, an extension in the B site coordination number from 6 to 8 is observed in the modulated phase. An interconnected 3D network of BO x polyhedra, similar to that of modulated CeNbO4.25, is obtained as a result of the structure modulation, which is not available in the unmodulated parent structure. Tracer diffusivity measurements indicate that the composition is an oxygen ion conductor, which relies on an intersticalcy conduction mechanism. Oxygen tracer diffusivity of 2.46 × 10 −9 cm 2 s −1, at 750 °C is reported.