Spontaneous polarisation induced effects, band structure and interband transition momentum evolution at the para-ferroelectric phase change of BaTiO3 and KNbO3

摘要: The tight-binding energy band structures of BaTiO3 and KNbO3 have been determined in the cubic tetragonal phases. modifications at para-ferroelectric change are analysed through orbital interactions. evaluation interband transition moment different points Brillouin zone reveals main transition, giving rise to first optical structure. Delta -band pairs which run nearly parallel determine dielectric properties. An matrix element investigation provides parameters anisotropy. evolution refractive index during phase is described decrease strengths along polar axis upward shift energies. polarisation-induced edge effects estimated connected with Bloch Experimental results on gap near for T>Tc associated precursor polarisation can be interpreted from this model. long- short-range interactions, expressed allow described.