Localized Proton Motions in Acceptor-Doped Barium Zirconates

Abstract

Acceptor-doped barium zirconates are currently accumulating considerable interest because of their high proton conductivity, especially in the intermediatetemperature range targeted for next-generation solid oxide fuel cells, combined with their excellent chemical stability. However, fundamental questions surrounding the proton conduction mechanism in these materials remain, for instance, regarding the nature of localized proton motions and how they depend on the local structural properties of the material. Here we investigate the nature of localized proton motions in the two acceptordoped proton-conducting perovskites BaZr 0.9 M 0.1 O 2.95 with M = Y and Sc, using quasielastic neutron scattering. We show the presence of pronounced localized proton dynamics, with mean residence periods on the time-scale of 1−30 ps and an activation energy of ∼100 meV for both materials. In view of first-principles calculations as reported elsewhere the experimentally established dynamics could comprise footprints from proton transfers as well as O−H rotational motions in several different types of proton sites due to a range of various local proton sites present in both materials.

Proton jump diffusion dynamics in hydrated barium zirconates studied by high-resolution neutron backscattering spectroscopy

“…These parameters were derived in our preceding experiments on 10Sc:BZO and 10Y:BZO. 6 With the chosen parameters the main features observed particularly well in the response of 10Sc:BZO are reproduced in the modelled IFWS signal; the presence of a peak in the temperature range of 300-400 K, a shi of this peak towards lower T for higher Q, and the take-off of the IFWS signal already Contrast plot of the IFWS response highlighting the maximum dependence on Q and T up to 600 K (a). Selected profiles at Q specific for the present experiment plotted in Fig.…”

“…approaching the Q-range in our preceding ToF experiments. [5][6][7] The detriment of NBS in comparison to NSE is the somehow reduced neutron ux on the sample making the characterization of some of the relaxation signals challenging, as we show hereaer.…”

“…Their hydrogen concentration, as determined from neutron diffraction with polarization analysis, are 0.34(3) (10Y:BZO), 0.18(2) (10Sc:BZO), 0.10(1) (10In:BZO), 0.20(1) (20In:BZO), and 0.19(1) (25In:BZO) mol mol Ba À1 . 6,7,10 The NBS experiments were conducted at the IN16B spectrometer of the Institut Laue Langevin (ILL) in Grenoble, France. 11,12 With an incident wavelength of 6.3Å and the Si(111) unpolished analyzer conguration a resolution of 0.9 meV and a maximum Q of 1.9Å À1 were accessed.…”

“…4 We showed in a series of preceding QENS experiments based on the time-of-ight (ToF) technique, that the response of the local dynamics of protons in Sc-, Y-and In-doped BZO is reminiscent of a jump motion between two and four equivalent sites. [5][6][7] These dynamics correspond to translations of protons between two adjacent oxygens and O-H reorientations, respectively. To access the required momentum transfers (Q) for monitoring the local dynamics the resolution of the spectrometers had to be relaxed to 0.2-0.6 meV.…”

Local structure and vibrational dynamics in indium-doped barium zirconate

“…At sufficiently high temperatures, typically above 300 K, the protons can diffuse throughout the lattice through a two-stage mechanism that involves the transferring (hopping) of a proton from one oxygen to another, neighboring, one and a reorientational motion of the -OH group between such a transfer. [6][7][8][9][10][11][12][13] However, fundamental questions encompassing the defect chemistry of these materials remain, especially in regard to the local coordination environment and dynamics of protons and in general the role of dopant atoms for the proton transport properties.…”