The temperature dependence of the93Nb nuclear quadrupole coupling constant in stoichiometric LiNbO3powder specimens was measured from 21 to 515deg;K. No phase transitions were observed in this range. Analysis of the data on a simple vibrational model gave an Einstein temperature of 514deg;K in excellent agreement with that calculated from the measured specific heat. Nonstoichiometric specimens showed a very rapid NQR line broadening with a small departure from stoichiometry, and they could not be studied in detail. The temperature dependence of the niobium coupling constant was found to be linearly correlated with the variation of the birefringence over the range minus;thinsp;80 to 200deg;C.
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