Local structure analysis of Ca in Ba1-xCaxTiO3 ceramics

Ba1-xCaxTiO3 (x=0.05) (BCTO) ceramics has larger spontaneous polarization, and a little higher Curie temperature Tc than BaTiO3 (BTO). It is considered that these dielectric characteristics are caused by Ca doped to A-site in BTO. We have studied the atomic position of Ca in BCTO by First-Principles calculations and Extended X-ray Absorption Fine Structure (EXAFS) analyses. In the First-Principles calculations, geometry optimizations were done assuming that Ca is located at A-site in BTO under a constrain symmetry. The obtained result suggested that the Ca in BCTO (x=0.125) located at A-site is off about 0.30 ?? from the Ba equilibrium position along [001] direction. We have performed the Ca K-edge and Ba L3-edge EXAFS experiments, using synchrotron radiation, to obtain the information of local displacement of the Ca in BCTO (x=0.05). Analyses of radial structure functions showed that the Ca in BCTO (x=0.05) had a larger Debye-Waller factor than Ba in the same specimen. The interatomic distance of Ca-O (2.68 ??) was shorter than that of the Ba-O (2.89 ??) in BCTO (x=0.05). The offcenter position of Ca predicted by the First-Principles calculations was confirmed by EXAFS technique.