Crystallographic aspects of the linear electro-optic effect

Aspects of symmetry and crystal chemistry of the linear electrooptic effect are analyzed on the basis of new experimental results. Relations between the linear electro-optic effect [r σ ijk] (unclamped) and the linear electrostrictive effect [d ijk] are investigated by comparison of the longitudinal effects r'111 and d'111; The relation |d'111|max/|r'111|max≥1 is valid for 41 of the hitherto available data of 49 crystals. Guidelines for the search of crystals with high electro-optic effects are reviewed. The most important keywords for a “chemical engineering” of new electro-optic materials are: pyroelectric symmetry groups; “polar” structural units; structures with strongly asymmetric bonds; molecules with high hyperpolarizabilities; structures tending towards a dielectric instability.