Abstract

There are many structure types of niobates, of which KNbO₃ (KN) with perovskite structure, Ba₂NaNb₅O₁₅ (BNN) with tungsten-bronze structure and LiNbO₃ (LN) are well-known NLO materials. It has been demonstrated that the deformed NbO₆ coordination octahedra in these materials are the basic structural units for the production of NLO effects.¹ The NbO₆ octahedra are deformed in different ways: i.e., a threefold axis deformation in LN, a twofold axis deformation in KN, and a mainly fourfold axis deformation in BNN. In the light of the anionic group theory of NLO effect,² of the three types of NbO₆ octahedron deformation, the one along a fourfold axis is the most advantageous. A broad survey of niobates containing deformed NbO₆ octahedra led to the discovery of new NLO material ZnLiNbO₄ (ZLN). ZLN possesses a spinel structure wherein the basic structural unit NbO₆ octahedron is deformed tetragonally. Although McCarthy and Keramidas reported its point group as 422,³ which implies that ZnLiNbO₄ exhibits no SHG effect, we observed large SHG effect in this compound.

© 1995 IEEE