Characterization of LiNbO3 by dilatometry and DTA.

DTA can successfully measure T(c) and hence the Li content for samples over most of the single phase range of LiNbO3. Above about 1190C, however, the enthalphy associated with the decomposition and melting of the near stoichiometric material masks the weak thermal change associated with T(c). Fortunately, dilatometry can be also used to detect T(c). The values of T(c) determined by these thermoanalytical techniques are 1129 +- 2 and 1198 +- 2C for the congruent and stoichiometric compositions. Careful dilatometric measurement of the thermal expansion in the temperature range from 350 to 1300K indicate that, while the a-axis expands continuously, the c-axis passes through a maximum at 640C for the congruent material and 700C for the stoichiometric material. Thermal expansion for the stoichiometric compared to the congruent composition is slightly greater along the c-axis and somewhat smaller along the a-axis. These expansions compensate to make the volume expansion of the two materials virtually identical.