Relationship between the Crystal Structure and Electrical Properties of Oxide Ion Conducting Ba3W1.2Nb0.8O8.6

Kirstie S McCombie; Eve J Wildman; Clemens Ritter; Ronald I Smith; Janet M S Skakle; Abbie C Mclaughlin

doi:10.1021/acs.inorgchem.8b01366

Relationship between the Crystal Structure and Electrical Properties of Oxide Ion Conducting Ba₃W_1.2Nb_0.8O_8.6

Inorg Chem. 2018 Oct 1;57(19):11942-11947. doi: 10.1021/acs.inorgchem.8b01366. Epub 2018 Sep 12.

Authors

Kirstie S McCombie¹, Eve J Wildman¹, Clemens Ritter², Ronald I Smith³, Janet M S Skakle¹, Abbie C Mclaughlin¹

Affiliations

¹ Department of Chemistry , University of Aberdeen , Meston Walk , Aberdeen AB24 3UE , United Kingdom.
² Institut Laue Langevin , 71 Avenue de Martyrs , BP 156, CEDEX 9 F-38042 Grenoble , France.
³ ISIS Facility , Rutherford Appleton Laboratory, Harwell , Didcot OX11 0DE , United Kingdom.

PMID: 30207462
DOI: 10.1021/acs.inorgchem.8b01366

Abstract

The oxide ionic conductor Ba₃W_1.2Nb_0.8O_8.6 has been synthesized as part of an investigation into the new class of Ba₃M'M''O_8.5 (M' = W, Mo; M'' = Nb) oxide-ion conducting hexagonal perovskite derivatives. The substitution of W⁶⁺ for Nb⁵⁺ in Ba₃W_{1+ x}Nb_{1- x}O_{8.5+ x/2} leads to an increase in the oxygen content, which enhances the low-temperature ionic conductivity. However, at 400 °C, the ionic conductivity of Ba₃W_1.2Nb_0.8O_8.6 is still significantly lower than the molybdenum compound Ba₃MoNbO_8.5. Remarkably, at 600 °C the bulk oxide ionic conductivities of Ba₃MoNbO_8.5, Ba₃WNbO_8.5, and Ba₃W_1.2Nb_0.8O_8.6 are very similar (σ_b = 0.0022, 0.0017, and 0.0016 S cm^-1, respectively). The variable-temperature neutron diffraction results reported here demonstrate that Ba₃W_1.2Nb_0.8O_8.6 undergoes a similar structural rearrangement to Ba₃MoNbO_8.5 above 300 °C, but the ratio of (W/Nb)O₄ tetrahedra to (W/Nb)O₆ octahedra rises at a faster rate upon heating between 300 and 600 °C. There is a clear relationship between the ionic conductivity of Ba₃M'_{1+ x}M''_{1- x}O_{8.5+ x/2} (M' = W, Mo; M'' = Nb) phases and the number of tetrahedrally coordinated M' and M ″ cations present within the crystal structure.