Pressure-induced changes in the electron density distribution in α-Ge near the α-β transition

Electron density distributions in alpha-Ge have been determined under high pressure using maximum entropy method with structure factors obtained from single crystal synchrotron x-ray diffraction in a diamond anvil cell. The results show that the sp(3) bonding is enhanced with increasing pressure up to 7.7(1) GPa. At higher pressures but below the alpha-beta transition pressure of 11.0(1) GPa, the sp(3)-like electron distribution progressively weakens with a concomitant increase of d-orbitals hybridization. The participation of d-orbitals in the electronic structure is supported by Ge K beta(2) (4p-1s) x-ray emission spectroscopy measurements showing the reduction of 4s character in the valence band at pressures far below the alpha-beta transition. The gradual increase of d-orbitals in the valence level in the stability field of alpha-Ge is directly related to the eventual structural transition. (C) 2015 AIP Publishing LLC.