Angewandte Chemie International Edition
© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Cover Picture (Angew. Chem. Int. Ed. Engl. 2/1994)
The cover picture shows a Fe3+-doped KNbO3 single crystal (formed from the orthorhombic, ferroelectric phase of KNbO3), which can be obtained from a molten K2O solution at 1050 °C, as well a matchstick for comparison (crystal growth: H. Wüest, ETH Zürich; photograph: M. Bischof, ETH Zürich). The crystals, which are yellow because of the doping with Fe3+ ions, can be used for information storage in a purely optical way (holography). Pure KNbO3 crystals are colorless and are applied in nonlinear optical materials to generate green and blue laser light. The critical review by J. Hulliger on p. 143 ff contains valuable information about crystal growth.