A brick layer model for surface conduction in porous ceramics

We provide herein a review and in-depth derivation and discussion of a surface brick layer model (SBLM) that scales the conductance of a surface layer – such as protonic conductance in adsorbed water – and the macroscopic conductivity for the porous material. The model is derived on basis of grains and pores of similar sizes and will be most realistic for porous compacts or loosely sintered ceramics of isotropic grains, although it still provides order-of-magnitude guidance also for textured or less porous materials. Brief comparison is made with other relevant models and literature. The model is illustrated and evaluated with data primarily from measurements of surface protonic conduction in porous nanoscopic ceramic oxides.