Revisiting the Crystal Structure of BaCe 0.4 Zr 0.4 Y 0.2 O 3−δ Proton Conducting Perovskite and Its Correlation with Transport Properties

BASBUS, JUAN F.; ARCE, MAURICIO D.; NAPOLITANO, FEDERICO R.; TROIANI, HORACIO E.; ALONSO, JOSÉ A.; SALETA, MARTÍN E.; GONZÁLEZ, MIGUEL A.; CUELLO, GABRIEL J.; FERNÁNDEZ-DÍAZ, MARÍA T.; SAINZ, MIGUEL PARDO; BONANOS, NIKOLAOS; JIMENEZ, CATALINA E.; GIEBELER, LARS; FIGUEROA, SANTIAGO J. A.; CANEIRO, ALBERTO; SERQUIS, ADRIANA C.; MOGNI, LILIANA V.

ACS Applied Energy Materials

ACS

Año: 2020 vol. 3 p. 2881 - 2892

2574-0962

Oxides with proton conductivity have a great potential forapplications in environmental energy technology. Despite the Ba￾Ce0.4Zr0.4Y0.2O3−δ (BCZY) perovskites being well-known proton conductors,it is a challenge to determine the optimal operating temperature range wherethe energy applications benefit most from this unique property. The protonictransport properties strongly depend on crystal structure and local distortionsin the participating cation coordination sphere, according to relatedtemperatures and gas feed. The transport and crystallographic properties ofBCZY were simultaneously studied by impedance spectroscopy (IS) andsynchrotron X-ray diffraction (S-XRD). A strong correlation betweenconductivity and the lattice parameter, corresponding in principle to a cubicsymmetry, was observed, mainly between 400 and 700 °C. The protonicconductivity range was analyzed by the H/D isotopic effect on the impedancespectra, which helped to identify protonic conduction as the governing transport mechanism below 600 °C, while the transport viaoxygen vacancies dominates above this temperature. In order to assess the real crystallographic structure, the simultaneousrefinement of laboratory XRD and neutron diffraction (ND) patterns was performed. According to this, BCZY changes fromrhombohedral symmetry below 400 °C to cubic at 600 °C in a second-order phase transition. Complementary quasielastic neutronscattering (QENS) enables us to determine a protonic jump length of 3.1 Å, which matches the O−O distances in the octahedraloxygen coordination sphere around the cations. These results support the protonic self-diffusion through proton hopping betweenintraoctahedral O sites as the main transport mechanism up to 600 °C.