Abstract
The ilmenite type NaNbO3 was prepared by low temperature hydrothermal reaction and had an endothermic phase transition at about 290°C and transformed to the perovskite type structure at about 485°C. The ionic conductivity, the lattice constants at high temperature and the latent heat were measured in order to investigate the phase transition at about 290°C. The crystal structure at 350°C was refined with the X-ray powder Rietveld method and the final R-factors were Rwp=24.1, Rp=18.4 and RB=14.5%. The refinement indicated that partial Na+ ions moved to the empty octahedral sites along the c-axis. From these results the phase transition at about 290°C was concluded to be the order-disorder transition of Na+ ions.
