Improved oxide-ion and lower proton conduction of hexagonal perovskite-related oxides based on Ba<sub>7</sub>Nb<sub>4</sub>MoO<sub>20</sub> by Cr<sup>6+</sup> doping

Oxide-ion conductors based on hexagonal perovskite-related oxide Ba7Nb4MoO20 have attracted much attention due to high oxide-ion and proton conductivities potential applications in many electrochemical devices such as solid fuel cells (SOFCs). Herein, we report simultaneous improvement of conductivity suppression by Cr6+ doping Ba7Nb4MoO20. New materials Ba7Nb4−xCrxMoO20+x/2 (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5) were synthesized. It was found that Ba7Nb3.8Cr0.2MoO20.1−δ (δ is the amount oxygen deficiency Ba7Nb3.8Cr0.2MoO20.1−δ) exhibits 1.6 × 10−3 S cm−1 at 508 °C 1.1 10−2 904 static air low transport number under wet conditions. also shows wide electrolyte domain partial pressure P(O2) regions from 1 2.2 10−27 atm (304 °C) 1.5 10−26 (604 °C), indicating extremely chemical electrical stability. The structure analyses shown a perovskite related 22 800 °C. refined crystal has oxygen-deficient cubic (c′) close-packed Ba(O1)2−y(O5)z layer where y vacancy tetrahedral O1 site z interstitial octahedral O5 site. Cr bond valence sum indicates an oxidation +6: Cr6+. cation located crystallographic near c′ layer, which leads excess conductivity, likely suppress conduction. Maximum-entropy method (MEM) demonstrated ions two-dimensionally migrate through lattice sites via interstitialcy diffusion mechanism °C, enables various oxides would be new strategy for