Abstract
The oxyhydride phase of barium titanate, BaTiO3−xHx, is a mixed hydride ion and electron conductor.
Highlights
Oxyhydrides, where a hydride ion (HÀ) is substituted on an oxygen site, are rare in nature and the oxyhydride phases (Ca,Sr,Ba)TiO3ÀxHx, which can form under strongly reducing conditions,[1,2] were the rst ones discovered based on the simple perovskite structure ABO3
We have shown that rst-principles calculations in combination with inelastic neutron scattering (INS) experiments are excellent tools to study the vibrational motion of the hydride ions and relate this to the character of the conduction electrons in oxyhydrides, and that chemical expansion can be used to discriminate between formation of delocalized bandstates and localized small polaron con gurations in these materials
In the present contribution we have investigated the character of conduction electrons in cubic BaTiO3ÀxHx, where an electron can form either a delocalized bandstate or localize as a small electron polaron on titanium bound next to a hydride ion
Summary
Oxyhydrides, where a hydride ion (HÀ) is substituted on an oxygen site, are rare in nature and the oxyhydride phases (Ca,Sr,Ba)TiO3ÀxHx, which can form under strongly reducing conditions,[1,2] were the rst ones discovered based on the simple perovskite structure ABO3. The aim of the present study is to investigate the possibility of polaron formation in bulk BaTiO3ÀxHx. We use two complementary techniques: rst-principles calculations based on density-functional theory (DFT) and inelastic neutron scattering (INS) experiments. Inelastic neutron scattering (INS) is used to study the vibrational motion of the hydride ion This experimental technique provides a straightforward way to investigate the vibrational properties of hydride ions because of the large neutron cross section of hydrogen relative to the other atomic species in BaTiO3ÀxHx. The vibrational spectrum is computed and to obtain accurate frequencies we make use of the hybrid functional HSE,[24,25] which is known to reproduce the experimental frequencies for BaTiO3 accurately.[26]. We nd that the electrons in bulk BaTiO3ÀxHx form delocalized bandstates, in contrast to ref. 7, and bulk BaTiO3ÀxHx should exhibit metallic-like conductivity
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