Invited Lecture
The effect of cation disorder on anion and cation transport in pyrochlore

Complex oxides often have multiple applications. Pyrochlores, for example, have been proposed for use both as nuclear energy materials and fast ion conductors. In both cases, cation disorder has been identified as a key factor enabling performance. In the case of nuclear applications, cation disorder has been linked to radiation tolerance while the same disorder is responsible for fast oxygen transport that makes pyrochlores interesting for fast ion conductor applications. Thus, transport, particularly that of oxygen, has been extensively studied in pyrochlores. However, there are still important questions regarding the relationship between cation disorder in mass transport in these types of materials.

Using both atomistic simulations and experiments, we examine how oxygen and cation transport in pyrochlore as a function of cation disorder. Using ion beam irradiation to induce cation disorder, we find that oxygen transport increases significantly as cation disorder increases. Atomistic simulations attribute this enhanced conductivity to increases in both the concentration and mobility of charged carriers responsible for ionic conductivity. In the case of cation transport, accelerated molecular dynamics simulations reveal a complex relationship between cation disorder and the mobility of cations. In particular, we find that cation transport is enhanced by cation disorder, but only once a critical level of disorder is achieved. We interpret this behavior in terms of the formation of a percolation network of disordered cations within an ordered matrix. These results provide new insight into the relationship between cation disorder and mass transport in these materials and suggest new routes for the development of materials for energy applications.