Congruent Composition and Li‐Rich Phase Boundary of LiNbO ₃

Abstract

The congruent composition of LiNbO 3 was determined precisely by correlating crystal growth compositions with the Curie temperatures of samples quenched from a melt before and after crystal growth and of various sections of crystals grown from that melt. The initial melt composition was determined by control of Li 2 CO 3 and Nb 2 O 5 contents. The melt compositions were varied from 47 to 49 mol% Li 2 O. The variation of T e with melt composition was found to follow T e = 9095.2 − 369.05C + 4.228C 2 , where C is mol% Li 2 O. High‐temperature DTA was used to determine T e with a precision of ±2°C. Above 1000°C the Li‐rich phase boundary was found to be a function of temperature by determining the weight gain after complete lithiation of congruently grown crystals. This boundary curves slightly toward lower Li 2 O content as temperature increases. The congruent composition of LiNbO 3 contains 48.45 mol% Li 2 O and has a measured Curie temperature of 1138°± 2°C.