Thermal Conductivity of an Isotopically Disordered Ferroelectric Crystal

Abstract

The thermal conductivity of a doped displacive ferroelectric crystal in the presence of an external electric field is investigated theoretically by double time thermal Green's function technique. The effect of the mass and force constant changes between impurity atoms and host lattice atoms along with the effect of higher order anharmonic and dipole moment terms is taken into account explicitely. It is found that the scattering processes due to mass change and the force constant change may mutually compensate each other's effect. The total thermal conductivity which is the sum of two terms contributed by optical and acoustical phonons is seen to increase with the applied electric field, which is in agreement with the experimental results of Steigmeier. In the vicinity of the Curie temperature, the thermal conductivity shows an anomalous behaviour and the soft mode is held responsible for that.