Neodymium substituted CaBi4Ti4O15 bismuth layered compound

In the present work, CaBi4−xNdxTi4O15 (0 ≤ x ≤ 1) ceramics were prepared and characterized. Although the substitution of Nd3+ for Bi3+ led to a decrease of tolerance factor t, the ferroelectricity in CaBi4−xNdxTi4O15 was not enhanced but weakened. With increasing x, the Curie temperature of CaBi4−xNdxTi4O15 was lowered and the peak of dielectric constant was significantly suppressed. Besides, the variation of lattice parameters of CaBi4−xNdxTi4O15 showed an approach of a and b, which revealed a development trend from ferroelectric orthorhombic structure to the prototype tetragonal structure with the substitution. This strongly suggested that Bi3+ is crucial for the ferroelectricity in four-layered CaBi4Ti4O15, just like found in two-layered Bi3TiNbO9 and three-layered Bi4Ti3O12 compounds. The importance of Bi3+ to the ferroelectricity should be due to the special electron configuration of Bi3+ but not its relatively small size, since Nd3+ is even smaller than Bi3+. The size mismatch between A-site cations and the provskite cuboctahedral cavity, indicated by t, seemed to play a secondary role in the contribution to the ferroelectricity of CaBi4Ti4O15 and its analogues. The dielectric properties of CaBi4−xNdxTi4O15 ceramics were also investigated at microwave resonant frequency.