Crystal structure and polarization properties of ferroelectric (SrxBi2.5−x/2Na1.5−x/2)Nb3O12 (x=0-1) ceramics

Crystal structure-polarization property relations in the (SrxBi2.5−x/2Na1.5−x/2)Nb3O12 (x=0-1) ceramics were investigated in this study. The atomic distances of Nb-O bonds, which compose the equatorial plane in the Nb(1)O6 and Nb(2)O6 octahedra, increased with increasing the composition x. The covalencies of Nb-O bonds in these octahedra decreased with the increasing atomic distances of the Nb-O bonds. The remanent polarization (Pr) of the samples was slightly improved by the Sr substitution for Bi and Na and the highest Pr value of 12.4 μC/cm2 was obtained at x=0.5. Also, the coercive field (Ec) of the samples varied from 68 to 44 kV/cm in the composition range of 0-0.5; it was recognized that the Sr substitution for Bi and Na was effective in improving the Ec values in this system. The Ec values were connected with the covalencies of Nb-O bonds in the Nb(1)O6 and Nb(2)O6 octahedra caused by the Sr substitution for Bi and Na. The Curie temperature (Tc) of (SrxBi2.5−x/2Na1.5−x/2)Nb3O12 ceramics drastically decreased from 610 to 61 °C with an increase in the tolerance factor and a decrease in the orthorhombicity, while anomalous variations in the dielectric constant were recognized in the composition range of 0-1.