The crystal structure and electrical properties of the oxide ion conductor Ba₃WNbO_8.5

Abstract

The crystal structure of the novel oxide ion conductor Ba3WNbO8.5.

The relationship between oxide-ion conductivity and cation vacancy order in the hybrid hexagonal perovskite Ba3VWO8.5

“…26 Furthermore, Ba 3 NbWO 8.5 exhibits similar conductivity to Ba 3 NbMoO 8.5 at 600 C and greater stability in a reducing 5% H 2 /N 2 atmosphere. 27 High oxide ion and proton conductivity has also been reported in Ba 7 Nb 4 MoO 20 , a hexagonal derivative with an average crystal structure composed of a disordered arrangement of 12R hexagonal perovskite and palmierite-like layers, similar to Ba 3 NbMoO 8.5 . 31 The structures of these cation-decient hexagonal perovskite derivatives are versatile and able to accommodate various transition metal cations, potentially enabling ionic conduction in different disordered layered systems.…”

“…23,26 Substantial oxide ion conductivity has been discovered in other compounds of the Ba 3 M 0 M 00 O 8.5 (M 0 ¼ Nb; M 00 ¼ Mo, W) family. [26][27][28][29][30] In particular, members of the Ba 3 Nb 1Àx V x MoO 8.5 series present enhanced ionic conductivity, with the x ¼ 0.1 composition showing a bulk conductivity of $0.01 S cm À1 at 600 C, one order of magnitude higher than the conductivity of Ba 3 NbMoO 8.5 . 26 Furthermore, Ba 3 NbWO 8.5 exhibits similar conductivity to Ba 3 NbMoO 8.5 at 600 C and greater stability in a reducing 5% H 2 /N 2 atmosphere.…”

High oxide ion and proton conductivity in a disordered hexagonal perovskite

“…Mixed combinations of corner-sharing and face-sharing octahedra can give rise to a variety of hexagonal perovskite derivatives able to accommodate cationic and anionic vacancies 27,28 . We have discovered significant oxide ion conductivity in Ba3NbMO8.5 (M = Mo, W), which exhibits a hybrid average structure intermediate between the 9R perovskite and palmierite structures 29,30 . Based on such findings, we have investigated the electrical and structural properties of Ba7Nb4MoO20, a cation-deficient 7H hexagonal perovskite derivative formed by an intergrowth of palmierite layers and 12R perovskite blocks 31 .…”

“…This disorder creates variable and dynamic MOx configurations accommodating the intrinsic anion vacancies and the protonic defects in Ba7Nb4MoO20, also assisting the ionic migration. The ionic conductivity in these hybrid systems is correlated with the relative average concentration of lower and higher coordination environments along the palmierite-like layers 30,33,48 , indicating that the ionic conductivity properties might be tailored by insertion of cations with preference for lower coordination geometries 49 . Other derivatives able to support ionic conduction could potentially be found among the members of the pseudo-ternary phase diagram of the Ba-Nb-Mo-O system (Supplementary Figure S4).…”

“…In addition, the ease of substitution of the M cations in these hexagonal derivatives could also lead to the generation of different hexagonal polytypes with diverse electrical properties 30,37,43 . The results presented here suggest that other layered cation-deficient hexagonal perovskites might support similar cation and anion disordered environments, favourable for significant ionic conduction.…”