On designing percolation proton conductors: A case study of (Sr,La)(Zr,Y)O2.95

Heavily acceptor-doped perovskite oxides have the potential to activate percolation conduction of protons at reduced temperatures, and the reported percolation proton conductors up to now are restricted to the systems containing high Sc content. However, larger trivalent rare earth elements (e.g., Y) are known to be better dopants for proton conducting zirconates, but their solubility is low. In this work, we propose a new strategy to design the percolation proton conducting perovskites, by introducing La and Y into the Sr and Zr-sites of SrZrO 3 , respectively, leading to the formation of (Sr 1.1- x La x -0.1 )(Zr 1- x Y x )O 2.95 (SLZY, x  = 0.1 – 1.0), which takes Pnma and Pna 2 1 orthorhombic structures with x  = 0.1 – 0.4 and 0.5 – 1.0, respectively. Interestingly, the conductivity decreases with the Y content increasing from 0.1 to around 0.7 and increases with the Y content further increasing to 1.0. Moreover, the activation energy of the bulk conduction shows the maximum value at x  = 0.6. In addition to the expected monotonically increasing activation energy resulted from the enhanced structural asymmetry, these results imply that the trapping effect of protons plays an important role, which is enhanced with Y content increasing from 0.1 to around 0.6. Notably, higher Y content (e.g., x  > 0.6) appears to activate the percolation conduction of protons, leading to the decreasing activation energy.