Optical birefringence study of the ferroelectric phase transition in lithium niobate tantalate mixed crystals: LiNb(1-x)Ta(x)O(3).

The optical birefringence of a complete solid-solution series of lithium niobate-tantalate crystals has been measured as a function of temperature. It is found that, irrespective of composition, the high-temperature paraelectric phase has a birefringence close to +0.063, suggesting that this value arises purely from the oxygen octahedra in the crystal structure. It is also observed that a small addition of lithium niobate to the tantalate produces a crystal that has zero birefringence at room temperature