Abnormal Curie temperature behavior and enhanced strain property by controlling substitution site of Ce ions in BaTiO3 ceramics

Dopants have a great effect on the phase transition behavior and the properties of the ferroelectrics. Here we report an abnormal Curie temperature (Tc) behavior and enhanced strain property by controlling the doping site of Ce ions in the BaTiO3 ceramics. The Ce doped A-site and B-site BaTiO3 ceramics (BT-xCe-A and BT-xCe-B, x=2, 4, 6, 8 mol%) were prepared by a conventional solid state reaction method through a different sintering temperature. The Raman test and the XPS results give evidence that Ce is successfully incorporated into Ba-site as Ce3+ in the BT-xCe-A samples, and into Ti-site as Ce4+ in the BT-xCe-B samples. Different doping sites have distinct phase transition behavior. Compared with the BT-xCe-A ceramics, the BT-xCe-B ceramics show higher Tc, and the Tc show abnormal increasing behavior with the increase of the Ce content. In the Ce doped BaTiO3 system, this phenomenon has not been reported before. The origin of the higher Tc and its increasing behavior is discussed from the viewpoint of the larger local strain field generated by the Ce4+ ions entering into B-site. Besides, the BT-xCe-B ceramics show a stronger diffuse phase transition behavior. The reason is considered that the Ce substituting B-site leads to a multiphase coexistence, which induces more frustration states for the polarization according to the random defect field theory. Due to such distinct phase transition behavior, the BT-xCe-B ceramics show the enhanced maximum polarization (Pmax) and enhanced strain properties compared with the BT-xCe-A ceramics. This work may provide a promising way to design high performance materials by controlling the substituting site of the dopant in other lead-free systems.