Microstructure, hydrogen distribution and electrical properties of melt grown high temperature protonic conductors
Résumé
A Sr3(Ca1+xNb2-x)O9-δ High Temperature Protonic Conductor has been produced using the melt growth process with the aim of reducing the grain-boundary blocking effect in proton conduction. The microstructure is characteristic of a cellular growth with cell dimension of 10–Click to view the MathML source in width and Click to view the MathML source in length. The cells have distinct core and shell regions. A composition gradient in bivalent to pentavalent cation ratio is observed from the core to the shell. The cores act as channels for hydrogen diffusion. Nano-scaled domains have been revealed inside the cells identified as domains of 1:1 order of the cations on the B sites and orientation variants in the oxygen octahedra tilting. Ion Beam Analyses using a Nuclear Microprobe reveal only a slight hydrolysis of the surface after heat treatment of 10 h at Click to view the MathML source in wet air. Protonic conductivity is discussed and improvements are suggested by optimizing the calcium to niobium ratio of the constituent elements and designing larger cells.