X-ray diffraction by a crystal in a permanent external electric field: electric-field-induced structural response in α-GaPO₄

Acta Cryst. (2006). A62, 1–10 [doi: 10.1107/S0108767305036111]

A permanent external electric field induces the displacements of atoms within a unit cell and variation of crystal lattice parameters. These microscopic changes causing dielectric polarization and converse piezoelectric effect can be observed experimentally by means of X-ray diffraction. The theory of X-ray diffraction in an E-field is developed and used for planning a synchrotron X-ray diffraction experiment. Based on 54 measured Bragg reflections, the electric-field-induced distortion of PO₄ and GaO₄ tetrahedra in α-GaPO₄ crystals was evaluated. It shows that the E-field-induced changes are larger at the PO₄ tetrahedra compared with those of GaO₄, which can be explained by the higher pseudoatomic charge of the P ion compared with Ga.

Semen Gorfman, Vladimir Tsirelson, Andreas Pucher, Wolfgang Morgenroth and Ullrich Pietsch