Microwave Dielectric Constants of Sodium-Ammonia Solutions

Measurements have been made of the complex dielectric constant ${\epsilon }^{\prime }-i{\epsilon }^{\prime \prime }$ of sodium-ammonia solutions at 10 GHz. The real part of the dielectric constant ${\epsilon }^{\prime }$ was a very dramatic function of solution concentration. At very low concentrations ${\epsilon }^{\prime }$ was close to the pure ammonia value, then increased slowly with concentration in the range $\chi =2\mathrm{}\times {10}^{-3\mathrm{}}$ to $\chi =2\mathrm{}\times {10}^{-2\mathrm{}}$. This increase has been attributed to the presence of permanent dipoles, and a dipole moment of approximately ${10}^{-16\mathrm{}}$ esu at room temperature was determined. At $\chi =2\mathrm{}\times {10}^{-2\mathrm{}}$ the value of ${\epsilon }^{\prime }$ decreased very abruptly to large negative values. This decrease is interpreted as the nonmetal to metal transition, indicating a very rapid decrease in the mass of the negatively charged carriers as the concentration is increased. In this same concentration range ${\epsilon }^{\prime \prime }$, the imaginary part of the dielectric constant, increased rapidly as would be expected from the increasing dc conductivity. Temperature-variation studies of the dielectric constant have also been made and are consistent with the known temperature behavior of the solution's conductivity, i.e., the lower the temperature the higher the concentration required to reach the metallic concentration region and hence produce a negative real part to the dielectric constant.