Page 40 - ILL Annual Report 2019

CHEMISTRY AND CRYSTALLOGRAPHY
Adrien Perrichon. French
Chalmers University of Technology, Sweden
‘ My research focuses on the investigation of “energy materials” using several neutron scattering
techniques (INS, QENS, NCS and ND) and first-principles calculations, specifically on complex non-stoichiometric oxides with proton or oxide-ion conducting properties.’
Local structure and vibrational dynamics of proton- conducting Ba In O (H O)
AUTHORS
A. Perrichon, L. Mazzei, S.M.H. Rahman and M. Karlsson (Chalmers, Göteborg, Sweden)
M. Jiménez-Ruiz (ILL)
ARTICLE FROM
J. Mater. Chem. A (2019)—doi: 10.1039/c9ta04056k
REFERENCES
[1] A. Jayaraman, A. Magrez, M. Caldes, O. Joubert, M. Ganne, Y. Piffard and L. Brohan, Solid State Ionics 170 (2004) 17
[2] J.-R. Martinez, C.E. Mohn, S. Stølen and N.L. Allan, J. Solid State Chem. 180 (2007) 3388
[3] R. Dervişoğlu, D.S. Middlemiss, F. Blanc, Y.-L. Lee, D. Morgan and C.P. Grey, Chem. Mater. 27 (2015) 3861
[4] L. Mazzei, A. Perrichon, A. Mancini, G. Wahnström, L. Malavasi, S.F. Parker, L. Börjesson and M. Karlsson, J. Mater. Chem. A 7 (2019) 7360
Structurally related to the acceptor-doped perovskites, the hydrated Ba2In2O5(H2O)x phases differ through the presence of extended static distortions. These distortions lead to the stabilisation of at least two distinct protons sites, H(1) and H(2) [1, 2], in a structure referred to as ‘pseudo-cubic’ (figure 1). Upon dehydration, oxygen vacancies tend to segregate to ultimately form the Ba2In2O5 brownmillerite phase.
We performed INS measurements on the IN1-Lagrange spectrometer on fully and partially hydrated Ba2In2O5(H2O)x phases. We also performed extensive AIMD simulations from which we calculated the vibrational densities of states, G(ħw), and the neutron scattering cross section, S(Q,ħw). By comparing the experimental and calculated S(Q,ħw), and the infrared (IR) spectra, we proposed an assignment of the spectra of the fully hydrated phase (figure 2a).
The bands (B), (D) and (G) are associated with the H(1) proton and correspond to the fundamental, degenerated δ(O-H(1)) wag modes, their overtones and the n(O-H(1)) stretch mode, respectively. For the H(2) protons, the ‘in-plane’ (C1) and ‘out-of-plane’ (C2) δ(O-H(2)) modes are clearly separated, with overtones (E1) and (E2), while the band (F) corresponds to n(O-H(2)). In particular, we showed that the (β) bands at 250 and 300 meV in the
2252x
Three-axis spectrometer IN1-Lagrange
Proton-conducting oxides are materials of huge interest for a variety of applications, such as electrolytes in membrane reactors or in proton-conducting fuel cells operating in the intermediate temperature T = 200–500 °C. Inelastic neutron scattering (INS) and ab
initio molecular dynamics (AIMD) simulations provide a powerful means of investigating the vibrational dynamics and local co-ordination of protons in these materials. This is essential for gaining insight into the microscopic mechanisms of proton diffusion, which allows for the rational design of materials with higher proton conductivity: a crucial requirement
for the development of new technologies.
ANNUAL REPORT 2019
Pseudo-cubic Brownmillerite
Figure 1
Schematic representation of the distorted layer of the brownmillerite- based Ba2In2O5(H2O)x, exhibiting hydrated ‘pseudo-cubic’ domains (left) and brownmillerite structured domains (right), respectively. InOX polyhedra in blue, oxygen atoms in red, H(1) protons in white, H(2) protons in yellow.