Local Structure and Its Impact on Ionic Conductivity in Cubic Perovskite Protonic Conductor, an Ab-Initio Based cluster Expansion Study
Authors: Zhang Lei , Liu Meilin 
Published: February 2020

Cubic perovskite of ceramics are typical parent structures for proton conducting electrolyte in intermediate-temperature solid oxide fuel cells, e.g. BZCYYb1. Proton conductivity within this type of materials is well known to be affected by hydration capability, as well as proton mobility. Although a few previous experimental characterizations2-5have unveiled a few pieces of information regarding local structures of proton, dopant and vacancy, a systematic and comprehensive understanding of the underline driving-force for local structure evolution is lacking. Similarly, typical ab-initioDFT calculations assume a fixed dopant concentration with very limited configurations in consideration6-12.
Atomically, local structure is the fundamental building-block that constitutively determines macroscopic hydration and mobility of ions. By carrying out ab-initiocalculations, with cluster expansion and Monte-Carlo simulations, competition between entropic-driven defect randomization and enthalpic-driven defect agglomeration is discovered. A temperature vs. dopant-concentration phase diagram is generated. Conductivity is a consequence of dopant, vacancy and proton interactions. Although trapping effects acting on vacancy and proton vary among dopants, a statistical average of ionic mobility is generated through the above approach. By using BaHfO3 as the prototype, representative dopants such as In, K, Sc, Y, Gd, Lu are taken as examples.
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