Crystal structure-polarization property relations in (Sr0.5-xCax)Bi2.25Na1.25Nb3O12 solid solutions

The relationship between crystal structure and polarization properties of (Sr0.5-xCax)Bi2.25Na1.25Nb3O12 solid solutions was investigated in this Study. A single phase of (Sr0.5-xCax)Bi2.25Na1.25Nb3O12 solid solutions was obtained over the whole composition range; the lattice parameters and the unit cell volume of (Sr0.5-xCax)Bi2.25Na1.25Nb3O12 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 Pr value of 16 mu C/cm(2) was obtained at x = 0.3. Thus, the variations in the P, value caused by the Ca substitution for Sr may be attributed to the variations in the covalency of Nb( 1)-O-6 bonds in the Nb(1)06 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. (c) 2007 Elsevier Ltd. All rights reserved.