15:30 〜 15:45
[19p-B301-9] Ultrafast Hydrogen Dynamics in Solid Oxide Observed by Infrared Pump-Probe Spectroscopy
キーワード：infrared pump-probe spectroscopy, proton dynamics in solid oxide, proton conductivity
Many kinds of oxide crystals include hydrogen as impurities. Since hydrogen in crystals changes the properties of oxides, many active studies have been carried out for a long time. Additionally, as the movement of hydrogen is the origin of proton conductivity in crystals, a detailed understanding of the proton dynamics in solid oxides, especially in perovskite-structured oxides, has been receiving increasing attention recently from the viewpoint of applications to solid oxide fuel cells. Hydrogen atoms in oxide crystals are supposed to form the covalent bond with the nearest oxygen atom and the weak hydrogen bond with the second nearest one. It is well known that O-H stretching frequencies correlate with O...O lengths and the resonant frequencies are in the range of 1000 - 3500 cm-1. Therefore, the infrared (IR) absorption spectroscopy is a useful tool to investigate the character of local hydroxyl environment in crystals. However, the usual linear IR spectroscopy gives only the static information of hydrogen. In order to get a better understanding of the vibrational dynamics of hydrogen, the nonlinear IR spectroscopic measurement, which enables us to probe the ultrafast proton dynamics, is necessary.
In this study, we carried out IR pump-probe measurement of deuterium in KTaO3 crystal. While the previous experiment was done for the same material with pico-second (ps) pulse laser, we used femto-second (fs) pulse laser. Since a fs laser pulse has a wide spectrum in frequency, it can stimulate not only the fundamental v: 0->1 transition, but also the transition from excited state, namely the excited state absorption (ESA) even there is the anharmonicity of the vibrational potential. As a result, we observed the v: 1->2 transition of O-D stretching mode. We measured the transient absorption change as a function of delay time and evaluated the decay time of the excited vibrational population. The measured results give the detailed information about the deuterium (and thus hydrogen) dynamics and the anharmonicity of the OD vibrational mode in KTaO3. Moreover, we measured the temperature dependence of IR absorption spectra of O-H and O-D modes by Fourier transform IR (FTIR) spectroscopy. By combining the result obtained by pump-probe measurement in time domain with that by FTIR in frequency domain, we discuss the mechanisms of vibrational energy decay and clarify the energy transfer channels of OD stretching mode in KTaO3.
In this study, we carried out IR pump-probe measurement of deuterium in KTaO3 crystal. While the previous experiment was done for the same material with pico-second (ps) pulse laser, we used femto-second (fs) pulse laser. Since a fs laser pulse has a wide spectrum in frequency, it can stimulate not only the fundamental v: 0->1 transition, but also the transition from excited state, namely the excited state absorption (ESA) even there is the anharmonicity of the vibrational potential. As a result, we observed the v: 1->2 transition of O-D stretching mode. We measured the transient absorption change as a function of delay time and evaluated the decay time of the excited vibrational population. The measured results give the detailed information about the deuterium (and thus hydrogen) dynamics and the anharmonicity of the OD vibrational mode in KTaO3. Moreover, we measured the temperature dependence of IR absorption spectra of O-H and O-D modes by Fourier transform IR (FTIR) spectroscopy. By combining the result obtained by pump-probe measurement in time domain with that by FTIR in frequency domain, we discuss the mechanisms of vibrational energy decay and clarify the energy transfer channels of OD stretching mode in KTaO3.