ION DOPING EFFECTS ON THE DIELECTRIC AND PHONON PROPERTIES OF (Ba, Sr)TiO3 THIN FILMS

The exact mechanism by which doping ions change the properties in (BST) thin films is not fully understood. We have shown based (Ba, Sr)TiO3 on the transverse Ising model including anharmonic spin-phonon interactions and using a Green's function technique that the dielectric constant and the phonon properties can be changed due to different exchange interactions between the doping ions and the host ions in BST thin films. They are highly dependent upon the magnitude and the kind of the stress (tensile or compressive) due to the different radii of the doping ions. The phonon energies can be larger or smaller for different doping ions, whereas their damping is always enhanced.