We propose a reaction model for the synthesis of YBa2Cu4O8 under normal pressure conditions, which contains 4 partial reaction steps. In a first step bariumnitrate and copperoxide
react to Ba2Cu3O5+δ. This substance will be formed for each mixtures Ba:Cu=2∶3...3∶2. The following two partial reaction steps are connected
to Ba2Cu3O5+δ, which reacts with Y2O3 and CuO to YBa2Cu4O8 or decomposes to BaCuO2 and CuO. In a last step parts of BaCuO2 reacts with Y2O3 and CuO to YBa2Cu4O8.