Theory of spontaneous polarization and birefringence in the tetragonal phase of KNbO₃

Abstract

The microscopic mechanism of optical anisotropy in the tetragonal phase of KNbO₃ is discussed taking account of the dipole-dipole effect due to the ionic and electronic polarizations of the crystal and the spontaneous Kerr effect. The last effect is a cause of the strong local field acting on the constituent ions. For the spontaneous polarization we use only the first effect. It is found that the birefringence and the spontaneous polarization are in good agreement with the experimental data.

Keywords:

• KNbO₃
• local field
• polarizability
• polarization
• Kerr effect
• birefringence