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

Abstract

BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ 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 BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ 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 BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ. At room temperature, the sample exhibits I4/mcm tetragonal symmetry, with cell parameters of a = 6.14911(7) Å and c = 8.87903(14) Å. The structure of BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ can be described by a distortion of the ideal cubic perovskite (a_p), resulting from the cooperative tilt of the (Zr,Ce,Y,Yb)O₆ octahedra along the [001]_p axis (tilt system a⁰a⁰c⁻). 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 Å. At around 650 °C, BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ undergoes a phase transition to the primitive cubic structure Pm$\overline{3}$m. 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 BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ obtained from neutron data have been deposited at the Cambridge Crystallographic Data Centre, CSD 2341244 (room temperature) and CSD 2341246–2341252 (100 to 700 °C).