Permittivity, dielectric loss and dc conductivity of NaNO3 crystals grown by epitaxy

The temperature dependence of the d.c. conductivity, the dielectric loss and the permittivity of NaNO3 single crystals prepared by epitaxial accretion of the (111) plane of NaNO3 on the (001) plane of mica were investigated. The measurements were performed in a temperature range from 20–300‡C. Below the melting point a region of intrinsic conductivity (UI=3·08 eV), caused by Na+ ions which are in interstitial sites, was observed. At lower temperature a region II (UII= 0·87 eV), where the conductivity is due to the presence of divalent impurities, probably Ca+ + followed (structurally sensitive region). Up to 250‡C polarization is observed, most probably due to ion and electron shifting only. Above that temperature the influence of the relaxed orientation of the NO3− groups becomes evident. At 275‡C the NO3s- groups behave in a completely disordered way as indicated by a sudden increase of the permittivity plotted against temperature.