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Protonic and electronic defects in the 12R-type hexagonal perovskite Sr₃LaNb₃O₁₂

Lookup NU author(s): Dr Alan Thursfield, Professor Ian MetcalfeORCiD, Dr Glenn Mather

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Abstract

The structural properties of the 12R-type hexagonal perovskite Sr3LaNb3O12 (space group R (3) over bar) have been examined by neutron diffraction and H-1 magic angle spinning-nuclear magnetic resonance (H-1 MAS-NMR). The latter technique supports the presence of protonic species in Sr3LaNb3O12 with bands at 5, 3.4 and 1.3 ppm. The electrical-transport properties of the nominally stoichiometric and acceptor-doped phases Sr3LaNb3-xMxO12-delta (M = Ti, chi = 0.1; M = Zr, chi = 0.03) have been analysed in the temperature range 550-900 degrees C by impedance spectroscopy in a selection of wet- and dry-gas atmospheres. Protons contribute increasingly to transport with decreasing temperature in wet air, as confirmed by an H+/D+ isotope effect, representing the first observation of proton conductivity in this structure type. The magnitude of the protonic transport increases with increasing acceptor-dopant concentration (x). A total conductivity value of 1.2 x 10(-8)S cm(-1) is reached at 650 degrees C for the Ti-doped phase in humidified air (pH(2)O approximate to 0.03 atm). The activation energy in wet air at 550-700 degrees C is slightly lower for the doped compositions (0.93 eV for the Zr-doped phase) in comparison to the nominally undoped material (1.13 eV). The origin of proton transport in the latter may originate from "self doping" of a small amount of Sr on the La sites. Conductivity is dominated by n-type charge carriers in reducing conditions, as confirmed by the observance of a -1/4 powerlaw dependency for pO(2) similar to 10(-8) atm. The activation energy of the title phase in the n-type region measured in 10% H-2:90% N-2 is 0.96 eV. In dry oxidising atmospheres, p-type charge carriers predominate (E-a = 1.42 eV) with the p-n transition occurring at pO(2) similar to 10(-4)atm. (C) 2013 Elsevier B.V. All rights reserved.

Publication metadata

Author(s): Tabacaru C, Aguadero A, Sanz J, Chinelatto AL, Thursfield A, Perez-Coll D, Metcalfe IS, Fernandez-Diaz MT, Mather GC

Publication type: Article

Publication status: Published

Journal: Solid State Ionics

Year: 2013

Volume: 253

Pages: 239-246

Print publication date: 15/12/2013

Online publication date: 07/11/2013

Acceptance date: 17/10/2013

Date deposited: 27/10/2014

ISSN (print): 0167-2738

ISSN (electronic): 1872-7689

Publisher: Elsevier BV

URL: http://dx.doi.org/10.1016/j.ssi.2013.10.031

DOI: 10.1016/j.ssi.2013.10.031

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