Electrical conduction in sodium nitrate crystals

Abstract

Abstract The anisotropy of electrical conduction in single crystals of sodium nitrate which belongs to the trigonal system is studied and the non-vanishing coefficients of the conductivity tensor are σ11 ═ σ22 ═ 7·08 × 10-10 Ω-1 cm-1 and σ33 ═ 1·32 × 10-9 Ω-1 cm-1 at 200 °C. The dependence of electrical conductivity on temperature can be represented by the expression σ ═ 2·98exp ( – 10930/T) + 4·16 × 1012 exp ( – 25280/T) Ω-1 cm-1, and can be approximated to two straight lines on the plot of logo σ against 1/T. These are interpreted as impurity influenced and intrinsic regions. Based on the experimental result that the conductivity decreased with the addition of divalent positive ion impurities, the mechanism of electrical transport is inferred to be via interstitial positive ion jumps with a jump activation energy of 0·94 eV. From the straight line for higher temperatures, the formation energy of Frenkel defect pair is deduced to be 2·46 eV. Effects of association of impurities with corresponding charge compensating point defects are discussed and a value of 0·5 eV appears to be reasonable for the association energy of the divalent positive ion impurity-positive ion vacancy complex. The divalent negative ion impurity-positive ion interstitial complex appears to be practically dissociated at room temperature. In the structure sensitive region, the positive ion interstitials that are responsible for the electrical transport appear to arise mostly as charge compensators for divalent negative ion impurities like SO2-4.