Vibrational Dynamics and Oxygen Diffusion in a Nanoporous Oxide Ion Conductor 12CaO·7Al2O3 Studied by 18O Labeling and Micro-Raman Spectroscopy (Vibrational dynamics and oxygen diffusion in a nanoporous oxide ion conductor 12CaO·7Al2O3 studied by18O labeling and micro-Raman spectroscopy)