Congruent Composition and Li-Rich Phase Boundary of LiNbO3

The congruent composition of LiNbO3 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 Li2CO3 and Nb2O5 contents. The melt compositions were varied from 47 to 49 mol% Li2O. The variation of Te with melt composition was found to follow Te= 9095.2 − 369.05C + 4.228C2, where C is mol% Li2O. High‐temperature DTA was used to determine Te 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 Li2O content as temperature increases. The congruent composition of LiNbO3 contains 48.45 mol% Li2O and has a measured Curie temperature of 1138°± 2°C.