In-situ neutron diffraction study of BaCe0.4Zr0.4Y0.2O3-δ proton conducting perovskite

BASBUS J.F.; ARCE M.D.; NAPOLITANO F.; ALONSO J. ; FENANDEZ DIAZ M. T.

Congreso; I Congreso Argentino de Técnicas Neutrónicas; 2017

Barium cerates and zirconates oxides are capable of transporting protonsthrough their crystal lattice. This feature makes them potential candidates ashydrogen sensors, membranes for hydrogen purification and isotopic exchange(hydrogen, deuterium, tritium -H/D/T-), electrolyte for proton conductor solidoxide fuel cell (PC-SOFC) and solid oxide electrolyzer cell (PC-SOEC).Recently, BaCe0.4Zr0.4Y0.2O3−d perovskite (BCZY) was proposed as material forthese applications. BCZY showed high bulk protonic conductivity and good CO2tolerance, being a good candidate to electrolyte for PC-SOFC, PC-SOEC,H2-purification membranes and H/D/T isotopic separation membranes.The structural information such as phase transitions, oxygen vacanciesconcentration, oxygen tilting and proton/deuterium sites locationand occupation allow to understand the behaviourof this compound at operating conditions. BCZY was synthesized by solid state reaction, calcined and sintered at1600 °C for 12 h. Crystal structure was studied by X-ray Diffraction (XRD) and Neutron Powder Diffraction (NPD).Previous study of the oxygen non-stoichiometry, linear expansion and electricalconductivity under oxidizing and reducing atmosphere revealed a complexbehavior below 500 °C. Non-linear expansion, hysteresis loops and changes ofelectrical properties depending of the atmosphere nature were observed. High TemperatureX-ray Diffraction (HT-XRD), linear thermal expansion and TG data indicate theslope change and hysteresis for BCZY under both atmospheres, between 300 and500 °C, are associated with the incorporation/loss of interstitial protons. Also,the H/D isotopic effect of BCZY was confirmed [1].Despite the HT-XRDreveals a non-linear change in the lattice parameter as a function of temperaturebetween 400 and 600 ºC, not phasetransition was detected by this technique. A High Temperature Neutron Powder Diffraction(HT-NPD) study was performed by combining thermodiffraction data collected atthe D1B and D2B beamlines of the ILL. A fully BCZY hydrated sample was heatedunder atmospheric air whereas NPD patterns were collected. HT-XRD suggest athat BCZY maintain a cubic symmetry at the whole range of temperature whereasHT-NPD indicated a phase transition from rhombohedral R-3c (167) to cubicsymmetry Pm-3m (221) above 400 °C[1]Basbus et al., J. Power Sources 329(2016) 262