Ultrasonic Study of NaNO2. I. Anisotropic Character of Elastic Constants and Attenuation Coefficients

The temperature dependence of the elastic constants c 11 , c 22 , c 33 , c 44 , c 55 and c 66 of NaNO 2 was determined in the wide temperature range from 20 to 200°C. Near the antiferroelectric transition temperature ( T N ), c 33 , c 44 , c 55 and c 66 are rather normal and show a slight bending at T N . On the other hand c 11 and c 22 show softening towards T N . Corresponding to the anisotropic behavior of the elastic constants, the ultrasonic attenuation coefficients associated with c 11 and c 22 exhibit critical behavior and those associated with c 33 and c 55 show normal temperature dependence. The above character in the elastic properties can be explained in terms of the anisotropic coupling constants between the elastic strains and the staggered polarization expected from a crystal symmetry consideration.