Temperature dependence of infrared phonon spectra in a sintered BaCeO3

Infrared reflection spectra of a sintered BaCeO3 are measured from 20 to 1000 cm−1 in temperature region from 23 to 1050 K. In high temperature, four broadened bands were observed, and in low temperature, each band splits into three bands characteristic of the orthorhombic structure. Based on estimated phonon frequency and phonon damping constant, a large fourth-order anharmonicity and smaller effective charge are proved against those of cubic perovskites. The important roles of the covalent character of host lattice and large phonon amplitude on the high proton (PR) conduction are discussed with respect to the high polarization of OH-molecule and the jumping of H+ ion. Similar behavior appears on high proton and superionic conductors.