The elastic, piezoelectric, and dielectric constants of sodium chlorate (NaCl${\mathrm{O}}_3$) and sodium bromate (NaBr${\mathrm{O}}_3$) have been measured over a wide temperature range. The value of the piezoelectric constant at room temperature is somewhat larger than that found by Pockels. The value of the Poisson's ratio was found to be positive and equal to 0.23 in constrast to Voigt's measured value of -0.51. At high temperatures the dielectric and piezoelectric constants increase and indicate the presence of a transformation point which occurs at a temperature slightly larger than the melting point. A large dipole piezoelectric constant (ratio of lattice distortion to dipole polarization) results for these crystals but the electromechanical coupling factor is small because the dipole polarization is small compared to the electronic and ionic polarization and little of the applied electrical energy goes into orienting the dipoles.

• Received 15 July 1946

DOI:https://doi.org/10.1103/PhysRev.70.529