Crystal structure-polarization property relations in (Sr_(0.5-x)Ca_x)Bi_(2.25)Na_(1.25)Nb_3O_(12) solid solutions

摘要

The relationship between crystal structure and polarization properties of (Sr_(0.5-x)Ca_x)Bi_(2.25)Na_(1.25)Nb_3O_(12) solid solutions was investigated in this study. A single phase of (Sr_(0.5-x)Ca_x)Bi_(2.25)Na_(1.25)Nb_3O_(12) solid solutions was obtained over the whole composition range; the lattice parameters and the unit cell volume of (Sr_(0.5-x)Ca_x)Bi_(2.25)Na_(1.25)Nb_3O_(12) solid solutions are linearly decreased with the Ca substitution for Sr. The decrease in the atomic distances of oxygen-oxygen bonds, which compose the equatorial plane, led to the decrease in the volume of the Nb(1)O_6 and Nb(2)O_6 octahedra caused by the Ca substitution for Sr. The covalency of the Nb( 1 )-O( 1) bond increased in the composition range of 0-0.3, while that of the Nb(1)-O(1') bond decreased in this composition range. The remanent polarizations (P_r) of the solid solutions were improved by the Ca substitution for Sr; the highest P_r value of 16 mu C/cm~2 was obtained at x=0.3. Thus, the variations in the P_r value caused by the Ca substitution for Sr may be attributed to the variations in the covalency of Nb(1)-O bonds in the Nb(1)O_6 octahedron, which is located the center of the pseudo-perovskite block. On the other hand, the coercive field (E_c) values of the solid solutions are in the order of approximately 45 kV/cm in the composition range of 0-0.5. Also, the Curie temperatures (T_c) of the solid solutions increased with increased the composition x; therefore, the increase in T_c value was connected with the decrease in the tolerance factor caused by the Ca substitution for Sr.