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 [rσijk] (unclamped) and the linear electrostrictive effect [dijk] 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.
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