The peoples of the world use huge amounts of energy, and most of it is fossil. To reduce the emissions the energy conversion efficiency should be as high as possible. One of the most promising technologies is solid oxide fuel cell (SOFC), however the cost should be reduced and the lifetime enhanced for SOFC to be widely used. Conventional SOFC conduct oxygen at high temperatures (1000 °C), this high temperature also make the cathode material work well. The lifetime of SOFC can increase if the operating temperature is decreased to intermediate temperatures (600 - 800 °C), however better cathode materials are needed to avoid tremendous loss from the reduction of oxygen gas occurring on the cathode. A suggested group of material for this application is layered double perovskites LnBaM\({}_{2}\)O\({}_{5+\delta}\) Ln, Ba, M, delta works with both H\({}^{+}\) and O\({}^{2-}\) electrolyte. One compound investigated YBaCo\({}_{2}\)O\({}_{5+\delta}\), solid state synthesis, structure, HT XRD, Rietveld, conductivity, thermal expansion, TGA. Conclusion