Synthesis and temperature dependence of the crystal structure of proton conductor BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb1711) by combined neutron and X-ray diffraction
Résumé
BaZr0.1Ce0.7Y0.1Yb0.1O3-delta is a widely studied proton conductor for solid oxide fuel cells but its structure has not been examined in detail. In this study, we synthesized a pure, well-crystallized BaZr0.1Ce0.7Y0.1Yb0.1O3-delta powder via a glycine-nitrate process. Using Rietveld analysis on X-ray and neutron diffraction powder patterns collected both at room temperature and at elevated temperatures, we investigate the crystal structure of BaZr0.1Ce0.7Y0.1Yb0.1O3-delta. At room temperature, the sample exhibits I4/mcm tetragonal symmetry, with cell parameters of a = 6.14911(7) & Aring; and c = 8.87903(14) & Aring;. The structure of BaZr0.1Ce0.7Y0.1Yb0.1O3-delta can be described by a distortion of the ideal cubic perovskite (a(p)), resulting from the cooperative tilt of the (Zr,Ce,Y,Yb)O-6 octahedra along the [001](p) axis (tilt system a(0)a(0)c(-)). Within the octahedra, it consists of a disordered arrangement of Zr, Ce, Y, and Yb atoms with an average distance (Zr,Ce,Y,Yb)-O of 2.219 & Aring;. At around 650 degrees C, BaZr0.1Ce0.7Y0.1Yb0.1O3-delta undergoes a phase transition to the primitive cubic structure Pm3m. This transition is characterized by a progressive decrease in the tilt angle, indicating a continuous phase transition, and is tricritical in nature. Crystallographic data for BaZr0.1Ce0.7Y0.1Yb0.1O3-delta obtained from neutron data have been deposited at the Cambridge Crystallographic Data Centre, CSD 2341244 (room temperature) and CSD 2341246-2341252 (100 to 700 degrees C).