High Oxide‐Ion Conductivity through the Interstitial Oxygen Site in Sillén Oxychlorides

Abstract

Oxide-ion conductors are gaining attention as future materials in energy applications, such as solid oxide fuel cells. Many Bi-containing compounds exhibit high oxide-ion conductivity via conventional vacancy mechanism. However, interstitial oxide-ion conduction is rare in Bi-containing materials. Herein, high oxide-ion conductivity is reported through interstitial oxygen sites in Sillén oxychlorides, LaBi 2−x Te x O 4+x/2 Cl (Bi 2 LaO 4 Cl-based oxychlorides). Oxide-ion conductivity of LaBi 1.9 Te 0.1 O 4.05 Cl is 20 mS cm −1 at 702 °C, and higher than best oxide-ion conductors as Bi 2 V 0.9 Cu 0.1 O 5.35 below 201 °C. Despite of the presence of Bi and Te species, LaBi 1.9 Te 0.1 O 4.05 Cl shows extremely high chemical and electrical stability at 400 °C from oxygen partial pressure 10 −25 to 0.2 atm and high chemical stability under CO 2 flow, wet 5% H 2 in N 2 flow, and air with natural humidity. Neutron scattering length density analysis, DFT calculations, and ab initio molecular dynamics simulations indicate that the extremely high oxide-ion conduction is attributed to cooperative diffusion through interstitial oxygen sites (interstitialcy diffusion mechanism) in triple fluorite-like layers. The present findings demonstrate the ability of LaBi 2−x Te x O 4+x/2 Cl as superior oxide-ion conductors, which can open new horizons for oxide-ion conductors.

High Conductivity and Diffusion Mechanism of Oxide Ions in Triple Fluorite-Like Layers of Oxyhalides

“…A similar oxide ion diffusion mechanism was also reported for Bi 1.9 Te 0.1 LaO 4.05 Cl. 28 Therefore, this mechanism is considered to be a common feature of the Silleń phase with a triple fluorite-like layer.…”

“…Mixed-anion compounds, which contain two or more anions, are of great interest because of the wide variety of structures and properties. − The oxyhalides are mixed-anion compounds containing both oxide ions and halide ions that exhibit a variety of material properties such as photocatalysis and magnetic properties. − Several oxyhalides such as La 0.9 Sr 0.1 O 0.45 F 2 and La 0.8 Sr 0.15 Mg 0.05 OBr 0.8 exhibit halide ion conduction. , On the other hand, oxide ion conduction in oxyhalides is rare and therefore worthy of study. − …”

Dimer-Mediated Cooperative Mechanism of Ultrafast-Ion Conduction in Hexagonal Perovskite-Related Oxides

“…The development of clean energy technologies, such as solid-oxide fuel cells (SOFCs) and proton ceramic fuel cells (PCFCs), is an essential path to achieve a carbon-neutral society. − When considering the cost and stability of SOFCs, it is important to lower the operating temperature because the high operating temperature causes the degradation due to undesirable chemical reactions and increases their costs. , Therefore, a high oxide-ion conductor that operates at low temperature is required. In addition to oxide-ion conductors, the transport and structural properties of proton conductors have been studied because they can exhibit high conductivity at intermediate temperatures due to the low activation energy for conductivity.…”

“…electrolyte domain is slightly narrowed. The slope in the low P(O 2 ) range between 1.2 × 10 −24 and 5.6 × 10 −21 atm at 908 °C has a negative value of −0.0276(5), implying n-type electronic conduction probably caused by partial reduction of Nb 5+ and/or Mo 6+ cations. Compared with Ba 7 Nb 4 MoO 20 , 13 the present Ba 7 Nb 3.8 Mo 1.2 O 20.1 sample shows a wide electrol y t e d o m a i n , s i m i l a r t o B a 7 N b 3 .…”

Three-Dimensional Visualization of Oxygen-Vacancy Migration and Redistribution in Ca-Substituted BiFeO3

“…Our model materials, Ca-doped bismuth ferrites with a significantly lower oxygen-migration activation energy, E A , have been exploited for many years. By creating solid solutions between orthorhombic CaFeO 2.5 (brownmillerite) and monoclinic BiFeO 3 (perovskite), defect engineering has emerged as a versatile tool for tuning the electronic and optoelectronic properties of these materials, meeting the practical demands of application in electrochromic sensors, resistive-switching memories, , solid-state fuel cells, − and batteries . BiFeO 3 -parent oxides undergo a ferroelectric-to-paraelectric transition with increasing calcium ion concentration.…”