Acceptor doping in the proton conductor SrZrO3

• Published in: Physical chemistry chemical physics : PCCP Vol. 19; no. 18; pp. 11485 - 11491
• Main Authors: Weston, Leigh, Janotti, A, Cui, X. Y, Stampfl, C, Van de Walle, C. G
• Format: Journal Article
• Language: English
• Published: United States Royal Society of Chemistry 10.05.2017
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c7cp01471f

Perovskite zirconates such as SrZrO 3 exhibit improved proton solubility and conductivity when doped with trivalent cations substituting at the Zr site. In this work, we present a detailed study of Sc and Y dopants in SrZrO 3 based on first-principles, hybrid density-functional calculations. When substituting at the Zr site (Sc Zr , Y Zr ), both dopants give rise to a single, deep acceptor level, where the neutral impurity forms a localized hole polaron state. The (0/−) charge transition levels are 0.60 eV and 0.58 eV above the valence-band maximum for Sc Zr and Y Zr , respectively. Under certain growth conditions, Sc and Y will form self-compensating donor species by substituting at the Sr site (Sc Sr , Y Sr ), and this is detrimental to proton conductivity. Due to its larger ionic radius, Y exhibits a greater tendency than Sc to self-compensate at the Sr site. We also investigated the proton-dopant association. The binding energy of a proton to a negatively charged acceptor impurity is 0.41 eV for Sc and 0.31 eV for Y, indicating that proton transport is limited by trapping at impurity sites. Acceptor dopants in proton-conducting oxides act as proton traps, or can accidentally incorporate as donors, reducing proton conductivity.