Neutron Scattering Study of the Anharmonic Lattice Vibrations in Calcium Fluoride

概要

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The half widths of the phonon energies of the acoustic modes propagating along the <111> axes of calcium fluoride, which is one of substances manifesting conspicuous anharmonicity in the temperature factor, have been measured at temperatures above 20K up to 573K with the thermal neutron scattering techniques. The individual phonon widths variously depend on temperature. The phonon widths at room temperature, about 1.5 to 2meV and 1.0meV for the longitudinal and transverse modes, respectively, are comparable to those observed hitherto in other substances. Therefore the conspicuous anharmonicity in the temperature factor does not generally implies the prominent phonon-phonon interactions. The former should rather be regarded as a result of the crystal symmetry on integral quantities. Anormalous line shapes have been observed for the longitudinal mode around q=0.4q_<max>. They probably reflect the frequency-dependent self-energy of the phonon.
社団法人日本物理学会の論文
1973-07-05