Hydrogen absorption in an epitaxial thin film of high-entropy perovskite oxide

We synthesized an epitaxial film of high-entropy perovskite oxide (HEPO) consisting of three elements (Ca, Sr, Ba) in the A site and 12 elements (Si, Ti, Cr, Mn, Fe, Co, Ni, Ge, Zr, Sn, Ce, Hf) in the B site of ABO(3), and investigated hydrogen absorption properties in the HEPO film. The hydrogen depth profile was measured by nuclear reaction analysis via the H-1(N-15, alpha gamma)C-12 reaction, showing the hydrogen absorption in the HEPO film with a maximum atomic concentration of 0.3 in the ABO(3) unit. The diffusion coefficient of H in the film was analyzed from the H depth profile, and the activation barrier for diffusion was estimated to be (0.54 +/- 0.13) eV. An absorption band was observed at 3290 cm(-1) in the infrared absorption spectrum, which corresponds to the O-H stretching vibration. Simultaneous measurements of nuclear reaction and resistance revealed that the HEPO film remained electrically insulating regardless of the hydrogen concentration. We demonstrated that hydrogen is incorporated in HEPO forming OH species while keeping HEPO electrically insulating.