Electric field dependence of inelastic scattering cross section of neutrons in doped displacive ferroelectrics

Abstract

Using the method of double-time temperature-dependent Green's functions, a general expression is derived for the one-phonon differential scattering cross section of neutrons in doped displacive ferroelectrics, in the presence of external electric field. 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 dipolemoment 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 width and shift in the frequency spectrum are dependent upon temperature, field and defect parameters. In the vicinity of the Curie temperature, the Cochran soft mode is held responsible for the anomalous behaviour of the scattering cross section.