Electric field induced charge density variations in partially-ionic compounds Original Research Article

Using a modulation technique and synchrotron radiation, we investigated the charge density variations in cubic ZnSe and trigonal SiO2 induced by an external high-electric field E applied along the [111] and [11.0] direction, respectively. Selecting particularly weak reflections, we observed an almost linear variation of the integrated intensity versus E changing by up to 2% at |E|=3 kV/mm. For both crystals, the displacements of the relative ion positions within the unit cell exceed the piezoelectric induced variation of the unit cell parameters by at least one order of magnitude. The measured intensity variations of ZnSe can be explained by the opposite displacement of the zinc and selenium ions towards the field direction breaking the stiff tetrahedral coordination of the chemical bond. For quartz, the electric field initiates a displacement of those oxygen ions only where the O–Si bond is directed oblique to the field direction. The other oxygen ions and the silicon positions remain nearly unchanged. Thus, the ionic arrangement is described mainly by a change in the O–Si–O bonding angles.