The dopant effects of introducing rare earth atoms into the LiNiVO4 inverse spinel structure were studied by measuring electrical conductivity of LiNiVO4 as a function of temperature, type of dopants, and dopant mole ratio. The dopant mole ratios of LiNiVO4 to Ln (where Ln = La, Gd or Yb) used in the reactions of LiNiVO4 and Ln(2)O(3) ranged from 1 x 10(6) to 1 x 10(2). Using a d.c. polarization method, the best improvement in conductivity was achieved by the smallest Yb-doped samples at 25 degrees C, an increase from 10(-10) to 10(-7) S/cm at a mole ratio of LiNiVO4:Yb = 10(4). They maintained high conductivity of 10(-7) S/cm up to a mole ratio of 10(2). From 10 degrees C to 50 degrees C, the medium Gd-doped samples reached their highest conductivity, ranging from 6.21 x 10(-7) to 3.52 x 10(-7) S/cm when the mole ratio was 10(4), but beyond that conductivity declined sharply to 10(-10) S/cm. At 25 degrees C, the largest La-doped samples showed only a slight increase in conductivity from 10(-9) to 10(-8) S/cm at a mole ratio of 10(4), much lower than 2.21 x 10(-6) S/cm measured by a pseudo a.c. non-polarization method. During the doping process at lower dopant concentrations, activation energy decreased as concentration increased, but it remained virtually constant at higher dopant concentrations due to the reactions between LiNiVO4 and the dopants.
