Anisotropic phonon precipitate scattering

The principal thermal conductivities of impure LaF 3 have been measured from 1.2 to 80K. The specimens contained large ( approximately 1 mu m) impurity precipitates in the trigonal basal plane. These precipitates caused the phonon scattering rate to be increased at T approximately 1K by a factor of approximately 85 when the temperature gradient was directed along the c axis and by approximately 3.5 when it was directed in the basal plane. The conductivity temperature dependences suggest that large precipitates scatter normal incidence phonons according to omega 0 and grazing incidence phonons according to omega 1 .