Deformations in Crystals Induced by External Electric Fields

This thesis presents the experimental study of electric-field-induced deformations in single crystals. It is well known that an external electric field applied to a piezoelectric crystals deforms the shape of the crystal on a macroscopic level. On the microscopic scale this deformation implies a change of the unit cell. Even though the relative change of the unit cell is small (Δd/d = 10−5 – 10−4), it can be measured by X-ray diffraction. The positions of the Bragg reflections are related to the unit cell parameters. Careful measurements of electric-field-induced changes in positions of Bragg reflections reveal the deformation of the unit cell. The intensities of the Bragg reflections are related to the electron density distribution in the unit cell, which reaches local maxima at the atomic positions. Displacements of atoms, rotations of molecules and polarization of the electron density change the diffracted intensities. Hence, careful measurements of electric field induced changes in diffracted intensities can reveal these deformations.