A layered ceramic conducts oxide ions at 233 degrees Celsius
A peer-reviewed materials study measured high bulk oxide-ion conductivity in a layered oxybromide at 233 degrees Celsius. Structural measurements and calculations indicated that ions mainly move through vacant crystal sites, despite excess oxygen in the material. Resistance between grains reduced total conductivity, leaving a practical constraint for lower-temperature fuel-cell electrolytes.
Science··Midday
Conductivity rises at a lower temperature
A layered ceramic carried oxide ions through its grains at 233 degrees Celsius with a conductivity of 0.01 siemens per centimetre. The peer-reviewed Nature Communications study examined Sillén oxybromides, materials combining bismuth-containing layers with bromine layers. The result concerns bulk conductivity inside the material. It points towards electrolytes for lower-temperature solid oxide fuel cells, whose electrolyte carries ions between electrodes, while grain boundaries reduced conductivity across the complete sample.[1], [2]
Extra oxygen accompanies vacant sites
Neutron diffraction found extra oxygen positions alongside vacancies at normal oxygen sites. Atomic-scale calculations and molecular dynamics simulations indicated that long-distance transport mainly involved ions hopping through those vacant sites, rather than extra ions pushing neighbouring ions onward. Electrical measurements, oxygen concentration cells and isotope tracing supported predominantly oxide-ion transport. Comparisons between wet and dry conditions indicated that proton conduction was not the dominant contribution.[1]
Grain boundaries constrain total transport
The material remained stable in tests involving oxidizing, reducing and carbon-dioxide-containing atmospheres, with no substantial chemical expansion detected as the atmosphere changed. At 300 degrees Celsius its electrical stability covered a broad range of oxygen partial pressures. Grain-boundary resistance nevertheless kept total conductivity below the bulk value, identifying grain growth and densification as areas needing improvement. A separate single-cell experiment tested power generation, while prolonged operation and compatibility with other components remain separate requirements.[1]
