Elementary energy bands concept for IV–VI crystals with phase transitions

Abstract

The possibility to describe the phase transformation in narrow-gap IV–VI-type semiconducting ferroelectrics, based upon the information about the symmetry of the elementary energy bands in the band structure of a given phase and the site symmetry of the related actual Wyckoff positions, is discussed. It is shown that the phase transition is accompanied by an increase of the degrees of freedom of the actual Wyckoff position as a result of the symmetry lowering. Such transformation in r-space is equivalent to the intervalley redistribution of free carriers due to electron–phonon coupling.

Keywords:

• Elementary energy bands
• Wyckoff positions
• IV–VI ferroelectrics
• GeTe