Electrical conductivity in sodium chlorate crystals

The electrical conductivity, σ of single crystals of sodium chlorate (m.p. 256 °C) grown from solution is studied in the temperature range 100 to 250 °C. A plot of lg (σT) against 1000/T gives a fairly continuous curve. It is resolved into three straight lines by a special graphical procedure. The experimental data can then be represented by σT = 2 x 10-4 e-6376/T + 8 x 109 e-19012/T +1029 e-41386/T. The addition of the divalent cationic impurity Ba2+ increased the conductivity between 130 and 80 °C, indicating a cation vacancy jump mechanism. The activation energy for the migration of cations is estimated to be 0.55 ± 0.02 eV and the energy of formation of thermal defects to be 2.18 eV. The conductivity changes are discussed in relation to the enhanced optical absorption coefficient in the long wavelength fundamental region and also in relation to the anomalous thermal expansion and dielectric constant of the crystal at the higher temperatures. Above 200 °C the conductivity increases at a higher rate. Several causes were considered and the effect is most probably due to products of thermal decomposition.