Influence of defect states on proton conductivity of Y-doped BaZrO3

Nuclear energy is a promising new energy to solve energy crisis. Separation and purification of hydrogen isotopes play an important role in the developing and utilizing of nuclear energy. BaZrO3-based oxide is an effective material for the separation and purification of hydrogen isotopes. In this paper, a series of BaZr1-xYxO3-delta (0 <= x <= 0.3) are synthesized by high-temperature solid state reaction method. The raw materials are calcined at 1200 degrees C for 5 h in air. Then the calcined powder is consolidated by an isostatic press and sintered at 1500 degrees C for 48 h in air, using a furnace equipped with aluminum oxide heater. Phase purity and phase structure of the obtained BaZr1-xYxO3-delta are analyzed by XRD. Results show that the structures of the BaZr1-xYxO3-delta are consistent with the BaZrO3 diffraction pattern (JCPDS 06-399). The Y ions are already incorporated into the lattice of BaZrO3, and the maximum doping concentration of Y rangs from 0.24 to 0.26. Besides, the proton conductivity of Y-doped BaZrO3 is determined under hydrogen atmosphere by the electrochemical impedance spectroscopy (EIS). Experiments show that the BaZr1-xYxO3-delta with 20 mol% Y has the highest conductivity of 0.0015 S/cm at 600 degrees C which is higher than that of the BaZrO3 matrix material by two orders of magnitude. As the concentration of Y increases, the strain in the crystal structure of BaZrO3 increases, which may be created by the defect of Y-doped BaZrO3. In order to reveal the mechanism of proton conduction in Y-doped BaZrO3, the influence of defect types on proton conduction is also investigated via photoluminescence (PL) and thermoluminescence (TL). For the BaZrO3 matrix, an asymmetrical broad emission peak at 350 to 650 nm occurs in PL with an excitation light of 334 nm. Analysis of Gaussian decomposition shows that the asymmetrical broad emission peak is created by two kinds of different oxygen vacancies ((V) over dot(O)), which are beneficial to proton conduction. Interestingly, when BaZrO3 is doped with Y, a new emission peak P1 at 388 nm appears owing to the negatively charged Y-Zr' of proton-trapping-type defects, which is harmful to the proton conduction in general. TL analysis shows that the number of Y-Zr' increases and the depth of the trap reduce, as the Y concentration increases in BaZr1-xYxO3-delta (x = 0, 0.05, 0.1, 0.2). Although the Y-Zr' is noxious for the proton conduction, the proton conductivity of BaZr1-xYxO3-delta (x = 0, 0.05, 0.1, 0.2) can be improved via the increase of the release ability of proton trapping as the depth of trap is reduced.