Speaker
Mrs
Carin Österberg
(Department of Physics, Chalmers University of Technology, Sweden)
Description
Proton conducting perovskite type oxides, such as BaTi1-xYxO3Hx, for which the protons are covalently bound to oxygens, are currently accumulating considerable attention. The proton conduction mechanism may be divided into two principal processes, hydrogen-bond mediated proton transfers (jumps) between neighbouring oxygen ions, and -OH reorientational motion between such transfers[1]. However, the local chemistry and structure, symmetry reduction, hydrogen-bonding interactions and proton-defect interactions etc., complicate the description about proton dynamics that is still not fully understood for even the simplest systems. A novel possibility to advance the understanding of hydrogen dynamics in perovskite materials is given by the recently discovered perovskite oxyhydrides ATiO3-xHx (A = Ba, Sr, Ca, x < 0.6)[2]. The hydrogens in oxyhydrides is of hydridic nature (H-) and take the place of oxygen vacancies rather than being covalently bound to oxygens.
In contrast with most other oxyhydrides, ATiO3-xHx are stable in air up to ca. 400 C, above which hydrogen is released. This observation leads to the conclusion that the hydride species in ATiO3-xHx have to be mobile. This finding is highly exciting because it implies that the perovskite structural framework can accommodate both, cation (proton) and anion (hydride) conduction.
Here, we report on investigations of both the local structure and dynamical behavior of the oxyhydride BaTiO3-xHx (x = 0.14 and 0.4), by means of inelastic (INS) and quasielastic neutron scattering (QENS). The INS results show two strong bands at 912 and 1027 cm-1 which are assigned to the Ti-H vibrations[3] and confirm the absence of a O-H band at approximately 3500 cm-1. Hence the results verify that the hydride-ions are located on vacant oxygen sites of the perovskite lattice. Subsequent measurements of the mean-square displacement of BaTiO3-xHx (x = 0.4) show a marked increase in the temperature range ca. 300-400 K, which indicates that there is a displacement reflecting the onset of diffusional H motion. Measurements of quasielastic spectra for T = 275-500 K indicate the presence of hydride-ion dynamics characterized by a relaxation time of the order of one nanosecond.
[1] M. Karlsson, Dalton Trans. 42 (2015) 317.
[2] Y. Kobayashi et al., Nature Mater. 11 (2012) 507.
[3] Y. Iwzaki et al., J. Appl. Phys. 108 (2010) 083705.
Primary author
Mrs
Carin Österberg
(Department of Physics, Chalmers University of Technology, Sweden)
Co-authors
Dr
Craig M. Brown
(NIST Center for Neutron Research, Gaithersburg, United States)
Dr
Madhusudan Tyagi
(NIST Center for Neutron Research, Gaithersburg, United States)
Dr
Maths Karlsson
(Department of Physics, Chalmers University of Technology, Sweden)
Mr
Reji Nedumkandathil
(Department of Materials and Environmental Chemistry, Stockholm University, Sweden)
Dr
Stewart F. Parker
(ISIS neutron source, Rutherford Appleton Laboratory, Oxfordshire, UK)
Prof.
Ulrich Häussermann
(Department of Materials and Environmental Chemistry, Stockholm University, Sweden)
