Recent studies have reported that the conductivity of La2Ce2O7 proton conductors is improved by aliovalent
doping, despite the high concentration of oxygen vacancies in the pristine material. In this study,
we provide new insights into the structural and conducting properties of La2-x AxCe2O7±d (A ¼ Naþ, Ca2þ,
Sr2þ, Ba2þ, Y3þ and W6þ; x 0.2). The materials are apparently single phase compounds with a disordered
fluorite-type structure by conventional X-ray diffraction; however, the local structure, studied by
Raman spectroscopy, reveals a biphasic mixture of fluorite and C-type phases, which depends on dopant
type and the sintering temperature. In addition, phase segregations are observed for Ca, Sr and Ba-doped
samples by scanning electron microscopy. The different substitutions do not improve the bulk conduction
at low temperature, and the conductivity differences between the samples are mainly ascribed to
microstructural changes. High sintering temperatures produce a significant reduction of the bulk conductivity,
i.e. 1.38 and 1.01 mS cm 1 at 300 C for samples sintered at 1400 and 1500 C, respectively. The
use of Zn as sintering aid greatly improves the densification of La2Ce2O7 at lower temperature, without
affecting negatively the conductivity.
