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.