Effect of phosphorus additions on the sintering and transport properties of proton conducting BaZr0.85Y0.15O3−δ

The influence of phosphorous additions on the sintering and electrical transport properties of the proton-conducting perovskite BaZr0.85Y0.15O3−δ (BZY) has been studied with a view to the use of phosphates as typical dispersants for the formation of stabilised solid suspensions or as possible sintering aids. P2O5 additions, (1−x)BZY·xP2O5, monotonously promote densification in the intermediate compositional range 0.04≤x≤0.08. Nonetheless, BZY reacts with phosphorous forming the phase Ba3(PO4)2 at temperatures as low as 600 °C. The associated loss of Ba from the perovskite, leads to a decrease in the perovskite lattice parameter, the formation of yttria-based impurity phases and impaired grain growth. Such reaction has an extremely detrimental effect on bulk and grain boundary conductivities. It is, therefore, vital that the current results are taken into account by the protonics community when attempting to prepare the stabilised solid suspensions of BZY nanopowders required for thin ceramic applications. Alternative dispersants to phosphate esters must be found.