PHASE RELATION OF SYSTEM LIVO3-NIO AND SOME PROPERTIES OF LINIVO4

The phase equilibrium relationship of the system LiVO3-NiO in the three component system Li2O-NiO-V2O5 was investigated by means of high and normal temperature X-ray diffraction techniques, thermogravimetric analysis, and differential thermal analysis. The phase diagram of the system LiVO2-NiO was constructed in the temperature range between 500° and 1550°C. The successive processes in air from a mixture of Li2CO3, NiO, and V2O5 to a spinel type compound LiNiVO4 proceeded through the formation of both LiNi(VO3), and LiVO3. The lattice constant of LiNiVO4 at 1000°C worked out at 8.220±0.001Å, whereas it was 8.217 Å at 700°C. About the change in the lattice constant it appeared that the cation arrangement in LiNiVO4 is (NixVl-x)N(LiNil-xVx)NO4 (l>x>0.15), so that the change may be caused by an increase in the concentration of Ni2+ ion in the tetrahedral sites. However, local occupancy ot Li+ in the four coordination positions and oxygen deficiency at high temperature are also possrtle, so that these may leave problems to be solved in future. For LiNiVO4 the electric conductivities over the temperature range from 250° to 1050°C and the thermoelectromotive forces at about 900°C were measured. Activation energies 1.48eV above 810°C and 0.557eV below 810°C came out from the electric conductivity measurements. Oxygen partial pressure dependence of the electric conductivity of LiNiVO4 was examined over the range 6×10-3 to l atm of Po. No correlation was gained in the Po ranges 6×10-5 to 4×10-3 and 1×10-1 l atm, but the electric conductivity was in proportion to Po-0.23 over Po 4×10-3 to 1×10-1 atm. © 1979, The Chemical Society of Japan. All rights reserved.