The influences of defect-induced phase transition on the morphology structure and electrical properties of Ni/Zn doped BaTiO3 ceramics

The BaTi 1- x (Ni 0.5 Zn 0.5 ) x O 3 ( x  = 0–0.10) ceramics are prepared by conventional sintering strategy. With increasing Ni/Zn co-doping, a continuous phase transition between BaTiO 3 (BT) polymorphs is demonstrated in this work. The phase composition evolution of orthorhombic(O)/tetragonal(T)-T/cubic(C)/hexagonal(H)-H phase can be observed in Ni/Zn co-doped BT ceramics. Owing to the successive transition of this phase structure, the micro morphology is modulated from normal circular grains to elongated morphology structure. Meanwhile, the strong ferroelectricity of the pure BT with O/T symmetry is gradually suppressed, and eventually disappears in the high-concentration Ni/Zn co-doped BT ceramics ( x  = 0.08, 0.10) with H symmetry. The oxygen vacancy defects induced by Ni/Zn acceptor doping at local Ti-sites are responsible for the continuous phase transformation. To maintain charge balance, A-site Ba vacancy and the reduction of Ti 4+ to Ti 3+ is generated and hence, the polar displacement of Ti-O ions is restrained in multiphase coexistence samples. For the low Ni/Zn content of x  = 0.02, the broadened phase transition region is advantageous for energy storage application. The energy storage density ( W rec ) of the x  = 0.02 sample is 0.49 J/cm 3 and corresponding energy efficiency ( η ) is 85 % at 140 kV/cm. The variation in electrical properties is closely associated with phase structure evolution and defects/defect dipoles caused by Ni/Zn co-doping. Our work is instructive for the design and engineering the phase composition and morphology structure of BT-based ceramics.