Comparison of Space-Charge Formation at Grain Boundaries in Proton-Conducting BaZrO3 and BaCeO3
Artikel i vetenskaplig tidskrift, 2017

Acceptor-doped BaZrO3 (BZO) and BaCeO3 (BCO) both exhibit considerable bulk proton conductivity, which makes them suitable as electrolytes in electrochemical devices. However, these materials display high grain-boundary (GB) resistance that severely limits the overall proton transport in polycrystalline samples. This effect has been attributed to the presence of space charges at the GBs, which form because of segregation of protons and charged oxygen vacancies. This blocking behavior is less prominent in BCO, but in contrast to BZO, BCO suffers from poor chemical stability. The aim with the present work is to elucidate why GBs in BZO are more resistive than GBs in BCO. We use density-functional theory (DFT) calculations to study proton and oxygen vacancy segregation to several GBs and find that the oxygen vacancy segregation energy is quite similar in both materials while the tendency for proton segregation is larger in BZO compared with that in BCO. This is not related to the GBs, which display similar proton formation energies in both materials, but because of different formation energies for protons in the bulk regions. This can be understood from a stronger hydrogen bond formation in bulk BCO compared with that in bulk BZO. Furthermore, segregation energies are evaluated in a space-charge model,. and the resulting space-charge potentials provide a consistent explanation of the experimentally observed difference in GB conductivity.

energy calculations

barium zirconate

ceramic fuel-cells

perovskites

band-gap

augmented-wave method

density-functional theory

oxides

defect segregation

stability

Författare

Anders Lindman

Chalmers, Fysik, Material- och ytteori

Edit Ahlberg Helgee

Chalmers, Fysik, Material- och ytteori

Göran Wahnström

Chalmers, Fysik, Material- och ytteori

Chemistry of Materials

0897-4756 (ISSN) 1520-5002 (eISSN)

Vol. 29 18 7931-7941

Ämneskategorier

Fysik

DOI

10.1021/acs.chemmater.7b02829

Mer information

Skapat

2017-10-20