Neutron Scattering and Nature of the Soft Optical Phonon in SrTiO_3

概要

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Measurement of neutron scattering from an SrTiO_3 crystal have been carried out in the temperature range from 4.5°K to 300°K. The integrated intensity of inelastically scattered neutrons due to excitation of the soft optical phonon was observed at various reciprocal lattice points at room temperature. The structure factors deduced from the observed intensities are in qualitative agreement with Slater's model of ionic movement. A strong anisotropy of the dispersion surface of the soft mode in reciprocal space was observed around q=0, the direction of the lowest frequency being along[100]. The intrinsic energy width of the soft mode shows a gradual in crease with increasing temperature from 0.22MeV(20°K) to 0.85MeV(250°K). The experimental results indicate that in SrTiO_3, the polarization fluctuation is entirely due to the excitation of optical phonons and the phonon system can be treated as a quasi-harmonic system over the temperature range from 4.5°K to 300°K.
社団法人日本物理学会の論文
1969-02-05