The congruent composition of LiNbO/sub 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/sub 2/CO/sub 3/ and Nb/sub 2/O/sub 5/ contents. The melt compositions were varied from 47 to 49 mol% Li/sub 2/O. The variation of T /SUB c/ with melt composition was found to follow T /SUB c/ = 9095.2 - 369.05C + 4.228C/sup 2/, where C is mol% Li/sub 2/O. High-temperature DTA was used to determine T /SUB c/ with a precision of + or - 2/sup 0/C. Above 1000/sup 0/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/sub 2/O content as temperature increases. The congruent composition of LiNbO/sub 3/ contains 48.45 mol% Li/sub 2/O and has a measured Curie temperature of 1138/sup 0/ + or - 2/sup 0/C.
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