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)O6 and Nb(2)O6 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 (Pr) of the solid solutions were improved by the Ca substitution for Sr; the highest Pr value of 16 μC/cm2 was obtained at x = 0.3. Thus, the variations in the Pr 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)O6 octahedron, which is located the center of the pseudo-perovskite block. On the other hand, the coercive field (Ec) 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 (Tc) of the solid solutions increased with increased the composition x; therefore, the increase in Tc value was connected with the decrease in the tolerance factor caused by the Ca substitution for Sr.