Characterization of LiNbO3 by Dilatometry and DTA

Abstract

DTA can successfully measure Tc and hence the lithium oxide content for samples over most of the single‐phase range of LiNbO3. Above 7sim;1190°C, however, the enthalpy associated with the decomposition and melting of the near stoichiometric material masks the weak thermal change associated with Tc. Fortunately, dilatometry can be also used to detect Tc. The values of Tc determined by these thermoanalytical techniques are 1130° and 1198°C for the congruent and stoichiometric compositions, respectively. Careful dilatometric measurement of the thermal expansion in the temperature range from 350 to 1300 K indicates that, while the a axis expands continuously, the c axis passes through a maximum at 640°C for the congruent material and 700°C 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.